International cal -Talent Search[1]

8/7/2019 International cal -Talent Search[1]

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International Mathematical Talent Search Round 1

Problem 1/1. For every positive integer , form the number , where is the sum of the digits of in base 10. Determine the minimum valueof in each of the following cases:

(i) (ii) (iii) (iv)

Problem 2/1. Find all pairs of integers, and , , such that thebinomial coefficients

form an increasing arithmetic series.

Problem 3/1. On an board we place dominoes, each covering twoadjacent squares, so that no more dominoes can be placed on the remainingsquares. What is the smallest value of for which the above statement istrue?

Problem 4/1. Show that an arbitrary acute triangle can be dissected bystraight line segments into three parts in three different ways so that eachpart has a line of symmetry.

Problem 5/1. Show that it is possible to dissect an arbitrary tetrahedron intosix parts by planes or portions thereof so that each of the parts has a plane of

symmetry.


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Problem 1/2. What is the smallest integer multiple of , other than itself, which contains only odd digits?

Problem 2/2. Show that every triangle can be dissected into nine convexnondegenerate pentagons.

Problem 3/2. Prove that if , and are pairwise relatively prime positiveintegers, and if

, then , , and are perfect squaresof integers.

Problem 4/2. Let , , , and be the areas of the triangular faces of atetrahedron, and let

,

,

, and

be the corresponding altitudes of thetetrahedron. If denotes the volume of the tetrahedron, prove that

Problem 5/2. Prove that there are infinitely many positive integers suchthat the box can not be filled completely with and solid cubes.


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Problem 1/3. Note that if the product of any two distinct members of is increased by , the result is the perfect square of an integer.Find the unique positive integer for which , , and arealso perfect squares.

Problem 2/3. Note that 1990 can be turned into a square by adding a digiton its right, and some digits on its left; i.e., . Prove that can not be turned into a square by the same procedure; i.e., there are no digits such that is a perfect square.

Problem 3/3. Find if , , , and are points on the sides of quadri-lateral so that

,

and the area of quadrilateral is exactly 52% of the area of quadri-lateral .

Problem 4/3. Let points with integer coordinates be given in the -plane.What is the minimum value of which will ensure that three of the pointsare the vertices of a triangle with integer (possibly, ) area?

Problem 5/3. Two people, and , play the following game with a deck of cards. With starting, and thereafter the players alternating, each playertakes either card or a prime number of cards. Eventually all of the cardsare chosen, and the person who has none to pick up is the loser. Who willwin the game if they both follow optimal strategy?


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Problem 1/4. Use each of the digits , , , , , , , , exactly twice toform distinct prime numbers whose sum is as small as possible. What mustthis minimal sum be? (Note: The five smallest primes are , , , , and .)

Problem 2/4. Find the smallest positive integer, , which can be expressedas the sum of distinct positive integers , , and , such that , , and are perfect squares.

Problem 3/4. Prove that a positive integer can be expressed in the form

if and only if it can also be expressed in the form ,where , , , and are positive integers.

Problem 4/4. Let be anarbitrary triangle, and construct ,

, and

so that each of the anglesmarked is . Prove that isan equilateral triangle.

Problem 5/4. The sides of measure , , and units. We fold italong , , and , where , , and are the midpoints of its sides,until , , and coincide. What is the volume of the resulting tetrahedron?


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Problem 1/5. The set consists of five integers. If pairs of distinct elementsof are added, the following ten sums are obtained: , , , , , , , , , . What are the elements of ?

Problem 2/5.Let and be integers, and form theforward differences of themembers of the sequence

1 3 9 27 812 6 18 54

4 12 368 24

16

and successive forward differences thereof, as illustrated on the right for thecase . Prove that all entries of the resulting triangle of positive

integers are distinct from one another.

Problem 3/5. In a mathematical version of baseball, the umpire chooses apositive integer , , and you guess positive integers to obtain infor-mation about . If your guess is smaller than the umpires , he calls it aball; if it is greater than or equal to , he calls it a strike. To hit ityou must state the correct value of after the rd strike or the th guess,whichever comes first. What is the largest so that there exists a strategythat will allow you to bat , i.e. always state m correctly? Describe yourstrategy in detail.

Problem 4/5. Prove that if is a non-constant real-valued function such that

for all real ,

, then is periodic. What isthe smallest . , such that for all ?

Problem 5/5. In , shown onthe right, let denote the radius ofthe inscribed circle, and let

,

,and

denote the radii of the circlestangent to the inscribed circle and tothe sides emanating from , , and , respectively. Prove that


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Problem 1/6. Nine lines, parallel to the base of a triangle, divide the othersides each into equal segments and the area into distinct parts. Findthe area of the original triangle, if the area of the largest of these parts is .

Problem 2/6. In how many ways can be expressed as the sum of oneor more consecutive integers?

Problem 3/6. Show that there exists an equiangular hexagon in the plane,whose sides measure , , , , , and units in some order.

Problem 4/6. An international firm has employees, each of whomspeaks several languages. For each pair of employees, , there is alanguage spoken by and not by , and there is another language spokenby and not by . At least how many languages must be spoken at the

firm?Problem 5/6. An infinite checker-board is divided by a horizontal lineinto upper and lower halves as shownon the right. A number of check-ers are to be placed on the boardbelow the line (within the squares).A move consists of one checker

jumping horizontally or verticallyover a second checker, and removingthe second checker.

What is the minimum value of

which will allow the placement of the lastchecker in row above the dividing horizontal line after moves? De-scribe the initial position of the checkers as well as each of the moves.


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Problem 1/7. In trapezoid ,the diagonals intersect at , the areaof is , and the area of is . What is the area oftrapezoid ?

Problem 2/7. Prove that if , , and are positive integers such that

, then both and are also expressible as the sums ofsquares of two positive integers.

Problem 3/7. For a positive integer, denote by the product of allpositive integers divisors of . Find the smallest for which

Problem 4/7. In an attempt to copy down from the board a sequence ofsix positive integers in arithmetic progression, a student wrote down the fivenumbers,

accidentally omitting one. He later discovered that he also miscopied one ofthem. Can you help him and recover the original sequence?

Problem 5/7. Let be a triangle with sides , , and and area . Denote by the triangle whose sides are the altitudes of (i.e.,

,

,

) and denote its area by . Similarly, let

be the triangle formed from the altitudes of , and denote

its area by

. Given that

= 30 and

, find .


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Problem 1/8. Prove that there is no triangle whose altitudes are of length , , and units.

Problem 2/8. As shown on the right,there is a real number , ,so that the resulting configuration yieldsa dissection of the unit square into sevensimilar right triangles. This must sat-isfy a monic polynomial of degree .Find that polynomial. (Note: A polyno-mial in is monic if the coefficient ofthe highest power of is .)

Problem 3/8. (i) Is it possible to rearrange the numbers

,

,

,

,

as , , , , so that all the numbers listed below are different?Prove your assertion.

(ii) Is it possible to rearrange the numbers , , , , , as , , , , , so that all the numbers listed below are different?Prove your assertion.

Problem 4/8. In a meter run, Anita can give at most a meter advantageto Bob and catch up with him by the finish line. In a meter run, Bob cangive at most a meter advantage to Carol and catch up with her by the endof the race. Assuming that all three of them always proceed at a constantspeed, at most how many meters of advantage can Anita give to Carol in a meter run and still catch up with her?

Problem 5/8. Given that , and are real numbers such that

determine .


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Problem 1/9. An grid is placed so that it has its corners at and . A legal move is defined as a move either one unit in the positive direction or one unit in the positive direction. The point , where and , is removed from the grid so that it is no longerpossible to pass through this point on the way to . How many possiblepaths are there from to ?

Problem 2/9. Given a point and two straight line segments on a rectangu-lar piece of paper in such a way that the intersection point of the straightlines does not lie on the paper. How can we construct the straight line with the help of a ruler if we are allowed to draw only within the limits ofthe paper?

Problem 3/9. A convex polygon has vertices which are colored so that

neighboring vertices are of different colors. Prove that one can divide thepolygon into triangles with non-intersecting diagonals whose endpoints areof different colors.

Problem 4/9. A triangle is called Heronian if its sides and area are integers.Determine all five Heronian triangles whose perimeter is numerically thesame as its area.

Problem 5/9. A set of five Trick Math Cubes is shown schematically onthe right. A magician asks you to roll them and to add the five numberson top of them. He starts adding them at the same time, and writes down thecorrect answer on a piece of paper long before you are finished with the task.

How does he do it? Expose and explain this trick.

179

278 377 872

971

773 780

186483 285

384

681741

543

642

345

147 840

960

168

366

564

861762

756

558

954

657

855 459


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Problem 1/10. Find if , and are positive integers such that

and

.Problem 2/10. Deduce from the simple estimate,

, that

.

Problem 3/10. For each positive integer , , determine a function

where

depend only on , such that

for and

Problem 4/10. A bag contains red balls and black balls. We

remove two balls at a time repeatedly and(i) discard them if they are of the same color,(ii) discard the black ball and return to the bag the red ball if they are differentcolors.

What is the probability that this process will terminate with one red ball inthe bag?

Problem 5/10. Let be a point on the circumcircle of , distinct from , and . Suppose meets at , and meets at . Let be the point of intersection of the circumcircles of and ,with . Prove that bisects the segment . (The various points

of intersection may occur on the extensions of the segments.)


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Problem 1/11. Express

in the form

, where and are positive

integers.

Problem 2/11. Let be a positive integer greater than . Show that at mosteight members of the set can be primes.

Problem 3/11. A convex -gon issaid to be rhombic if all of its sidesare of unit length and if its oppositesides are parallel. As exemplified onthe right (for the case of ),a rhombic -gon can be dissectedinto rhombi of sides in several dif-

ferent ways. For what value of

cana rhombic -gon be dissected into666 rhombi?

Problem 4/11. Prove that if three of the interior angle bisectors of a quadri-lateral intersect at one point, then all four of them must intersect at that point.

Problem 5/11. Let . Find thepolynomial, , of smallest degree for which

and

.


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Problem 1/12. A teacher writes a positive integer less than fifty thousand onthe board. One student claims it is an exact multiple of ; a second studentsays it is an exact multiple of ; and so on, until the twelfth student says thatit is an exact multiple of . The teacher observes that all but two of thestudents were right, and that the two students making incorrect statementsspoke one after the other. What was the number written on the board?

Problem 2/12. A regulardodecagon is inscribedin a square of area as shown on the right,where four vertices ofthe dodecagon are at the

midpoints of the sides ofthe square. Find the areaof the dodecagon.

Problem 3/12. Let be a set of points in the plane, with the property thatthe distance between any pair of distinct points in is at least . Define tobe a largest possible subset of such that the distance between any pair ofdistinct points in is at least

. How many points must be in ?

Problem 4/12. Prove that if

is a zero of a cubic polynomial withinteger coefficients, then it is the only real zero of that polynomial.

Problem 5/12. In the figure on

the right,

and

are paral-lel lines, is perpendicular tothem, and are the in-tersection points of

and

witha circle of diameter greater than and center, , on the seg-ment . Prove that the prod-uct is independent of thechoice of on the segment .


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Problem 1/13 Milo is a student at Mindbender High. After every test, hefigures his cumulative average, which he always rounds to the nearest wholepercent. (So would round down to , but would round up to .) Today he had two tests. First he got in French, which dropped hisaverage by point. Then he got in History, which lowered his averageanother points. What is his average now?

Problem 2/13 Erin is devising a game and wants to select four denomina-tions out of the available denominations $1, $2, $3, $5, $10, $20, $25, and$50 for the play money. How should he choose them so that every valuefrom $1 to $120 can be obtained by using at most seven bills?

Problem 3/13 For which positive integers is it possible to color the integerswith red and blue so that no two red points are a distance apart, and no two

blue points are a distance apart?

Problem 4/13 Prove that there are infinitely many ordered triples of positiveintegers such that .

Problem 5/13 Armed with just a compass no straightedge draw twocircles that intersect at right angles; that is, construct overlapping circles inthe same plane, having perpendicular tangents at the two points where theymeet.


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Problem 1/14. Let be positive numbers such that

. Prove that .

Problem 2/14. The price tags on three items in a store are as follows:

$ 0.75 $ 2.00 $5.50

Notice that the sum of these three prices is $8.25, and that the product ofthese three numbers is also . Identify four prices whose sum is $8.25and whose product is also .

Problem 3/14. In a group of eight mathematicians, each of them finds thatthere are exactly three others with whom he/she has a common area of in-terest. Is it possible to pair them off in such a manner that in each of the

four pairs, the two mathematicians paired together have no common area ofinterest?

Problem 4/14. For positive integers and , define to mean that is the square of an integer. Prove that if , then there exists a positiveinteger such that and .

Problem 5/14. Let be given, extend its sides, and construct twohexagons as shown below. Compare the areas of the hexagons.


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Problem 1/15. Is it possible to pair off the positive integers , , , , in such a manner that the sum of each pair of numbers is a different primenumber?

Problem 2/15. Substitute different digits ( , , , , ) for different lettersin the following alphametics to ensure that the corresponding additions arecorrect. (The two problems are independent of one another.)

H A R R I E T D I A N AM A R R I E D A N D

H E R S A R A HD E N T I S T A R E

R E B E L S

Problem 3/15

. Two pyramids share a seven-sided common base, with ver-tices labeled as

,

,

, ,

, but they have different apexes, and . No three of these nine points are colinear. Each of the edges

and

( ), the diagonals of the common base, and the seg-ment are colored either red or blue. Prove that there are three segmentsamong them, all of the same color, that form a triangle.

Problem 4/15. Suppose that for positive integers and , the equa-tions and are satisfied. Prove that

and determine when equality holds.

Problem 5/15. Let

and

be two circles intersecting at the points and , and let

be a circle through , with center at . Determine, with proof,conditions under which the common chord of

and

is tangent to

?


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Problem 1/16. Prove that if , then .

Problem 2/16. For a positive integer

, let

be the product of thenonzero base 10 digits of . Call prodigitious if divides . Showthat one can not have a sequence of fourteen consecutive positive integersthat are all prodigitious.

Problem 3/16. Disks numbered through are placed in a row of squares,with one square left empty. A move consists of picking up one of the disksand moving it into the empty square, with the aim to rearrange the disks inthe smallest number of moves so that disk is in square , disk is in square , and so on until disk is in square and the last square is empty. Forexample, if the initial arrangement is

3 2 1 6 5 4 9 8 7 12 11 10

then it takes at least moves; i.e., we could move the disks into the emptysquare in the following order: , , , , , , , , , , , , , .

What initial arrangement requires the largest number of moves if ?Specify the number of moves required.

Problem 4/16. Let be an ar-bitrary convex quadrilateral, with , , , the midpoints of its sides,as shown in the figure on the right.

Prove that one can piece together tri-angles , , , to form a parallelogram congruent toparallelogram .

Problem 5/16. An equiangular octagon has sides of length ,

, ,

, , , , . Given that , find the length of .


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Problem 1/17. The digit number, , was obtainedby listing the integers from to in succession. We are to remove ofits digits, so that the resulting number is as large as possible. What are thefirst digits of this digit number?

Problem 2/17. Find all pairs of positive integers for which .

Problem 3/17. Show that it is possible to arrange in the plane points sothat no of them will be the vertices of a convex pentagon. (A polygon isconvex if all of its interior angles are less than or equal to .)

Problem 4/17. A man is years older than his wife. He noticed years agothat he has been married to her exactly half of his life. How old will he be

on their

th anniversary if in

years she will have spent two-thirds of herlife married to him?

Problem 5/17. What is the minimum number of rectangles that willcover a square? The rectangles may overlap each other and/or theedges of the square. You should demonstrate your conclusion with a sketchof the covering.


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Problem 1/18. Determine the minimum length of the interval such that for all real numbers for which .

Problem 2/18. For a positive integer , let denote the product ofthe positive integer divisors (including 1 and ) of . Find the smallest forwhich .

Problem 3/18. The graph shown onthe right has vertices, edges,and each vertex is of order (i.e., ateach vertex edges meet). Some ofthe edges are labeled , , , , as shown. Prove that it is possibleto label the remaining edges , , , , so that at each vertex the sumof the labels on the edges meeting atthat vertex is the same.

Problem 4/18. Let be distinct real numbers such that

Find the value of the expression

Problem 5/18. Let and be twolines in the plane, and let be apoint as shown in the figure on theright. Using only a compass and anunmarked straight edge, construct anisosceles right triangle , so that is on line , is on line , and is the hypotenuse of .


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Problem 1/19. It is possible to replace each of the signs below by either or so that

At most how many of the signs can be replaced by a sign?

Problem 2/19. We say is a primitive Heronian triple if , , and are positive integers with no common factors (other than ), and if the areaof the triangle whose sides measure , , and is also an integer. Prove thatif , then and must both be odd.

Problem 3/19. The numbers in the rectangle shown on the rightwere obtained by putting together the

distinct dominoes of a standardset, recording the number of dots,ranging from to on each side ofthe dominoes, and then erasing theboundaries among them. Determinethe original boundaries among thedominoes. (Note: Each domino con-sists of two adjoint squares, referredto as its sides.)

Problem 4/19. Suppose that satisfies the functional equation

Find .

Problem 5/19. In the figure onthe right, determine the area of theshaded octogon as a fraction of thearea of the square, where the bound-aries of the octogon are lines drawnfrom the vertices of the square to themidpoints of the opposite sides.


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Problem 1/20. Determine the number of points on the hyperbola

for which both and are integers.

Problem 2/20. Find the smallest value of for which the following state-ment is true: Out of every set of positive integers one can always chooseseven numbers whose sum is divisible by .

Problem 3/20. The husbands of mathematicians accompany their wivesto a meeting. Sometimes the husbands pass one another in the halls, butonce any particular pair have passed each other once, they never pass eachother again. When they pass one another, either only one of them recognizes

the other, or they mutually recognize each other, or neither recognizes theother. We will refer to the event of one husband recognizing another one asa sighting, and to the event of them mutually recognizing each other as achat, since in that case they stop for a chat. Note that each chat accountsfor two sightings.

If sightings take place, prove that one of the husbands must have had atleast two chats.

Problem 4/20. Suppose that and are positive integers such that the frac-tions and , when rounded (by the usual rule; i.e., digits andlarger are rounded up, while digits and smaller are rounded down) to threedecimal places, both have the decimal value .

Find, with proof, the smallest possible value of .

Problem 5/20. In the figure shownon the right, the centers of circles

,

, and

are collinear, and arethe points of intersection of

and

, and is point of intersection of

and the extension of . Provethat the two small circles shown, tan-gent to

and , and

and , respectively, are congruent

to one another.


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Problem 1/21. Determine the miss-ing entries in the magic squareshown on the right, so that the sum ofthe three numbers in each of the threerows, in each of the three columns,and along the two major diagonals isthe same constant, . What is ?

33

31 28

Problem 2/21. Find the smallest positive integer that appears in each of thearithmetic progressions given below, and prove that there are infinitely manypositive integers that appear in all three of the sequences.

Problem 3/21. Rearrange the integers , , , , , , into a sequence

,

,

,

, ,

,

, so that the absolute value of the difference of

and

is either or for each , , , , , .

Problem 4/21. Assume that the infinite process, shown in the first figure be-low, yields a welldefined positive real number. Determine this real number.

Problem 5/21. Assume that , shown in the second figure above,is isosceles, with . Let and be points onsides and , respectively, so that and .Determine, with proof, .


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Problem 1/22. In nobody could claim that on their birthday their agewas the sum of the digits of the year in which they were born. What was thelast year prior to which had the same property?

Problem 2/22. Determine the largest positive integer for which there is a

unique positive integer such that and

isa positive integer.

Problem 3/22. Assume that there are million telephones in current usein the United States. Is it possible to assign distinct -digit telephone num-bers (with digits ranging from to ) to them so that any single error indialing can be detected and corrected? (For example, if one of the assignednumbers is 8128772917 and if one mistakenly dials 8128722917, thennone of the other numbers which differ from 8128722917 in a single digit

should be an assigned telephone number.)

Problem 4/22. As shown in the first figure below, a large wooden cube hasone corner sawed off forming a tetrahedron . Determine the lengthof , if , and area .

Problem 5/22. As shown in the second figure above, in a square of base there is one circle of radius

, there are two circles of radius

, and thereare three circles of radius

. All circles are tangent to the lines and/or to one

another as indicated, and the smallest circle goes through the vertex of thetriangle as shown. Determine

,

, and

.


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Problem 1/23. In the addition prob-lem on the right, each letter repre-sents a different digit from to .Determine them so that the resultingsum is as large as possible. What isthe value of with the resultingassignment of the digits?

Problem 2/23. We will say that the integer is fortunate if it can be ex-pressed in the form , where and are integers. Prove that if is fortunate, then so is .

Problem 3/23. Exhibit in the plane straight lines so that they intersect

one another in exactly

points. Assume that it is permissible to have morethan two lines intersect at some points. Be sure that your solution should beaccompanied by a carefully prepared sketch.

Problem 4/23. Prove that .

Problem 5/23. Isosceles triangle has been dissected into thirteenisosceles acute triangles, as shown in the two figures below, where all seg-ments of the same length are marked the same way, and the second figureshows the details of the dissection of . Given that the base angle, ,of is an integral number of degrees, determine .


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Problem 1/24. The lattice points ofthe first quadrant are numbered asshown in the diagram on the right.Thus, for example, the th latticepoint is , while the th lat-tice point is . Determine, withproof, the th lattice point in thisscheme.

Problem 2/24. Let

be the digit number (inbase ), formed from copies of and copies of . Prove that

isnot divisible by for any value of , , , .

Problem 3/24. In , let , , , and as-sume that and are points chosen on sides and , respectively,so that and quadrilateral have the same area and the sameperimeter. Determine the square of the length of the segment .

Problem 4/24. Determine the positive integers for which

Problem 5/24. Let be a convex planar polygon with vertices, and fromeach vertex of construct perpendiculars to the sides (or extensionsthereof) of not meeting at that vertex. Prove that either one of these per-pendiculars is completely in the interior of or it is a side of .


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Problem 1/25. Assume that we have rods, each units long. They areto be cut into pieces measuring , , and units, so that the resulting piecescan be assembled into triangles of sides , , and units. How should therods be cut?

Problem 2/25. Let be a polynomial with integer coefficients, and as-sume that and . Prove that is not a perfect square.

Problem 3/25. One can show that for every quadratic equation there exist constants , and , with , such that the equation is equivalent to the original equation, and the faultyreasoning either or must equal to yields the correct answers or .

Determine constants

, and

, with

, so that the equation

can be solved in such manner.

Problem 4/25. Assume that is a scalene triangle, with as itslongest side. Extend to the point so that is between and on theline segment and . Prove that is obtuse.

Problem 5/25. As shown in the fig-ure on the right, is a pyramid,whose base, , is a rhombus with

. Assume that

. Prove that .


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Problem 1/26. Assume that x,y, and z are positivereal numbers that satisfy the equations given on the

right.

x + y + xy = 8,

y+

z+

yz= 15

,z + x + zx = 35.

Determine the value of x + y + z + xyz.

Problem 2/26. Determine the number of non-similar regular polygons each

of whose interior angles measures an integral number of degrees.

Problem 3/26. Substitute different digits

(0, 1, 2, . . . , 9) for different letters in the al-phametics on the right, so that the corre-

sponding addition is correct, and the result-

ing value of M O N E Y is as large aspossible. What is this value?

S H O W

M E

+ T H EM O N E Y

Problem 4/26. Prove that ifa b c > 0, then

2a + 3b + 5c 83

ab +

bc +

ca 1

3

a2

b+

b2

c+ 4

c2

a

.

Problem 5/26. Let ABCD be a con-vex quadrilateral inscribed in a circle,

let M be the intersection point of thediagonals ofABCD, and let E,F,G,and H be the feet of the perpendicu-lars from M to the sides of ABCD,as shown in the figure on the right.

Determine (with proof) the center of

the circle inscribable in quadrilateral

EFGH.

M

C

B

F

EA

H

D G


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Problem 1/27. Are there integers M,N ,K, such that M + N = K and

(i) each of them contains each of the seven digits 1, 2, 3, . . . , 7 exactly once?

(ii) each of them contains each of the nine digits 1, 2, 3, . . . , 9 exactly once?

Problem 2/27. Suppose that R(n) counts the number of representations ofthe positive integer n as the sum of the squares of four non-negative integers,where we consider two representations equivalent if they differ only in the

order of the summands. (For example, R(7) = 1 since 22 + 12 + 12 + 12 isthe only representation of 7 up to ordering.)

Prove that ifk is a positive integer, then R(2k

) + R(2k+1

) = 3.

Problem 3/27. Assume that f(1) = 0, and that for all integers m and n,

f(m + n) = f(m) + f(n) + 3(4mn 1).Determine f(19).

Problem 4/27. In the rectangular coordinate plane, ABCD is a square, and(31, 27), (42, 43), (60, 27), and (46, 16) are points on its sides, AB,BC,CD,and DA, respectively. Determine the area of ABCD.

Problem 5/27. Is it possible to construct in the plane the midpoint of a given

segment using compasses alone (i.e., without using a straight edge, except

for drawing the segment)?


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Problem 1/28. For what integers b and c is x =

19 +

98 a root of theequation x4 + bx2 + c = 0?

Problem 2/28. The sides of a triangle are of length a,b, and c, where a,b,and c are integers, a > b, and the angle opposite to c measures 60. Provethat a must be a composite number.

Problem 3/28. Determine, with a mathematical proof, the value of x; i.e.,the greatest integer less than or equal to x, where

x = 1 +1

2+

13

+1

4+

15

+ + 11, 000, 000

.

Problem 4/28. Let n be a positive integer and assume that for each integerk, 1 k n, we have two disks numbered k. It is desired to arrange the2n disks in a row so that for each k, 1 k n, there are k disks betweenthe two disks that are numbered k. Prove that

(i) ifn = 6, then no such arrangement is possible;

(ii) ifn = 7, then it is possible to arrange the disks as desired.

Problem 5/28. Let S be the set of all points of a unit cube (i.e., a cube each

of whose edges is of length 1) that are at least as far from any of the verticesof the cube as from the center of the cube. Determine the shape and volume

ofS.


29/44


Problem 1/29. Several pairs of positive integers (m, n) satisfy the equation19m +90+8n = 1998. Of these, (100, 1) is the pair with the smallest valuefor n. Find the pair with the smallest value for m.

Problem 2/29. Determine the smallest rational numberr

ssuch that

1

k+

1

m+

1

n r

swhenever k,m, and n are positive integers that satisfy the inequality

1

k+

1

m+

1

n< 1.

Problem 3/29. It is possible to arrange eight

of the nine numbers

2, 3, 4, 7, 10, 11, 12, 13, 15in the vacant squares of the 3 by 4 arrayshown on the right so that the arithmetic av-

erage of the numbers in each row and in each

column is the same integer. Exhibit such an

arrangement, and specify which one of the

nine numbers must be left out when complet-

ing the array.

1

9

14

5

Problem 4/29.Show that it is possible to arrange seven distinct points in the

plane so that among any three of these seven points, two of the three points

are a unit distance apart. (Your solution should include a carefully preparedsketch of the seven points, along with all segments that are of unit length.)

Problem 5/29.The figure on the

right shows the ellipse

(x 19)219

+(y 98)2

98=

1998.

Let R1, R2, R3, and R4 denote those

areas within the ellipse that are inthe 1st, 2nd, 3rd, and 4th quadrants,

respectively. Determine the value of

R1 R2 + R3 R4.

100 200-100

-200

200

400

RR

RR

2

1

3

4

y

x


30/44


Problem 1/30. Determine the unique pair of real numbers (x, y) that satisfythe equation

(4x2 + 6x + 4)(4y2 12y + 25) = 28.

Problem 2/30. Prove that there are infinitely many ordered triples of positive

integers (a,b,c) such that the greatest common divisor of a,b, and c is 1, andthe sum a2b2 + b2c2 + c2a2 is the square of an integer.

Problem 3/30. Nine cards can be numbered using positive half-integers

(1/2, 1, 3/2, 2, 5/2, . . . ) so that the sum of the numbers on a randomly cho-sen pair of cards gives an integer from 2 to 12 with the same frequency of

occurence as rolling that sum on two standard dice. What are the numbers

on the nine cards and how often does each number appear on the cards?

Problem 4/30. As shown in the fig-

ure on the right, square PQRSis in-scribed in right triangle ABC, whoseright angle is at C, so that Sand P areon sides BC and CA, respectively,while Q and R are on side AB. Provethat AB 3QR and determine whenequality holds.

S

A Q R B

P

C

Problem 5/30. In the figure on the

right, ABCD is a convex quadri-lateral, K,L,M, and N are themidpoints of its sides, and PQRSis the quadrilateral formed by the

intersections of AK, BL, CM,and DN. Determine the area ofquadrilateral PQRS if the area ofquadrilateral ABCD is 3000, andthe areas of quadrilaterals AMQPand CKSR are 513 and 388, re-spectively.

PQ

RS

BMA

L

D

K

N

C


31/44


Problem 1/31. Determine the three leftmost digits of the number

11 + 22 + 33 + + 999999 + 10001000.

Problem 2/31. There are infinitely many ordered pairs (m, n) of positiveintegers for which the sum

m + (m + 1) + (m + 2) + + (n 1) + nis equal to the product mn. The four pairs with the smallest values ofm are(1, 1), (3, 6), (15, 35), and (85, 204). Find three more (m, n) pairs.

Problem 3/31. The integers from 1 to 9 can be arranged into a 3

3 array sothat the sum of the numbers in every row, column, and diagonal is a multiple

of9.

(a) Prove that the number in the center of the array must be a multiple of 3.

(b) Give an example of such an array with 6 in the center.

Problem 4/31. Prove that if0 < x < /2, then

sec6 x + csc6 x + (sec6 x)(csc6 x) 80.

Problem 5/31. In the figure shown on the

right, O is the center of the circle, OK andOA are perpendicular to one another, Mis the midpoint ofOK, BN is parallel toOK, and AMN = NMO.

Determine the measure ofABN in de-grees.

M

N

O

A

B

K


32/44


Problem 1/32. Exhibit a 13-digit integer N that is an integer multiple of213

and whose digits consist of only 8s and 9s.

Problem 2/32. For a nonzero integer i, the exponent of 2 in the prime fac-torization of i is called ord2(i). For example, ord2(9) = 0 since 9 is odd,and ord2(28) = 2 since 28 = 2

27. The numbers 3n1 for n = 1, 2, 3, . . .are all even, so ord2(3

n 1) 1 for n > 0.a) For which positive integers n is ord2(3

n 1) = 1?b) For which positive integers n is ord2(3

n 1) = 2?c) For which positive integers n is ord2(3

n 1) = 3?Prove your answers.

Problem 3/32. Letf

be a polynomial of degree98,

such thatf(k) =

1

kfor

k = 1, 2, 3, . . . , 99. Determine f(100).

Problem 4/32. Let A consist of16 elements of the set {1, 2, 3, . . . , 106}, sothat no two elements of A differ by 6, 9, 12, 15, 18, or 21. Prove that two ofthe elements ofA must differ by 3.

Problem 5/32. In ABC, let D, E, and F be the midpoints of the sides ofthe triangle, and let P,Q, and R be the midpoints of the corresponding me-dians, AD,BE, and CF, respectively, as shown in the figure below. Provethat the value of

AQ2 + AR2 + BP2 + BR2 + CP2 + CQ2

AB2 + BC2 + CA2.

does not depend on the shape ofABC and find that value.

E

P

D

Q

R

A B

C

F


33/44


Problem 1/33. The digits of the three-digit integers a, b, and c are the ninenon-zero digits 1, 2, 3, . . . , 9, each of them appearing exactly once. Giventhat the ratio a : b : c is 1 : 3 : 5, determine a, b, and c.

Problem 2/33. Let N = 111 . . . 1222 . . . 2, where there are 1999 digits of1followed by 1999 digits of2. Express N as the product of four integers, eachof them greater than 1.

Problem 3/33. Triangle ABC has angle A measuring 30, angle B mea-suring 60, and angle C measuring 90. Show four different ways to dividetriangle ABC into four triangles, each similar to triangle ABC but with onequarter of the area. Prove that the angles and sizes of the smaller triangles

are correct.

Problem 4/33. There are 8436 steel balls, each with radius 1 centimeter,stacked in a tetrahedral pile, with one ball on top, 3 balls in the second layer,

6 in the third layer, 10 in the fourth, and so on. Determine the height ot the

pile in centimeters.

Problem 5/33. In a convex pentagon ABCDE the sides have lengths 1, 2,3, 4, and 5, though not necessarily in that order. Let F, G, H, and I bethe midpoints of sides AB, BC, CD, and DE, respectively. Let X be themidpoint of segment F H, and Y be the midpoint of segment GI. The length

of segment XY is an integer. Find all possible values of the length of sideAE.


34/44


Problem 1/34. The number N consists of 1999 digits such that if each pairof consecutive digits in N were viewed as a two-digit number, then thatnumber would either be a multiple of 17 or a multiple of 23. The sum of the

digits ofN is 9599. Determine the rightmost ten digits ofN.

Problem 2/34. Let C be the set of non-negative integers which can be ex-pressed as 1999s + 2000t where s and t are also non-negative integers.(a) Show that 3, 994, 001 is not in C.(b) Show that if0 n 3, 994, 001 and n is an integer notin C, then 3, 994, 001 n is in C.

Problem 3/34. The figure on the right shows

the map of Squareville, where each city block

is of the same length. Two friends, Alexandra

and Brianna, live at corners marked by A andB, respectively. They start walking toward eachothers house, leaving at the same time, walking

with the same speed, and independently choos-

ing a path to the others house with uniform dis-

tribution out of all possible minimum-distance

paths (that is, all minimum-distance paths are

equally likely). What is the probability that they

will meet?

A

B

Problem 4/34. In P QR, P Q = 8, QR = 13,and RP = 15. Prove that there is a point S on theline segment P R, but not at its endpoints, such thatP Sand QSare also integers.

S

P Q

R

Problem 5/34. In ABC, AC > BC,CM is the median, and CH is the al-titude emanating from C, as shown inthe figure on the right. Determine the

measure of MCH, if ACM and

BC H each have measure 17

.H B

C

MA


35/44


Problem 1/35. We define the repetition number of a positive integer n tobe the number of distinct digits of n when written in base 10. Prove thateach positive integer has a multiple which has a repetition number less than

or equal to 2.

Problem 2/35. Let a be a positive real number, n a positive integer, anddefine the power towera n recursively with a 1 = a, a (i + 1) = aaifor i = 1, 2, . . . . For example, we have 4 3 = 444 = 4256, a number whichhas 155 digits. For each positive integer k, let xk denote the unique positivereal number solution of the equation x k = 10 (k + 1). Which is larger:x42 or x43?

Problem 3/35. Suppose that the 32 computers in a certain network arenumbered with the 5-bit integers 00000, 00001, . . . , 11111 (bit is short forbinary digit). Suppose that there is a one-way connection from computer

A to computer B if and only if A and B share four of their bits with theremaining bit being a 0 at A and a 1 at B. (For example, 10101 can sendmessages to 11101 and to 10111.) We say that a computer is at level k in thenetwork if it has exactly k 1s in its label (k = 0, 1, 2, . . . 5). Suppose furtherthat we know that 12 computers, three at each of the levels 1, 2, 3, and

4, are malfunctioning, but we do not know which ones. Can we still be sure

that we can send a message from 00000 to 11111?

Problem 4/35. We say that a triangle in the coordinate plane is integral ifits three vertices have integer coordinates and if its three sides have integer

lengths.

(a) Find an integral triangle with a perimeter of 42.

(b) Is there an integral triangle with a perimeter of 43?

Problem 5/35. We say that a finite set of points is well scattered on the

surface of a sphere if every open hemisphere (half the surface of the sphere

without its boundary) contains at least one of the points. While {(1, 0, 0),(0, 1, 0), (0, 0, 1)} is not well scattered on the unit sphere (the sphere ofradius 1 centered at the origin), but if you add the correct point P, it becomeswell scattered. Find, with proof, all possible points P that would make theset well scattered.


36/44


Problem 1/36. Determine the unique 9-digit integer M that has the follow-ing properties: (1) its digits are all distinct and non-zero; and (2) for every

positive integer m = 2, 3, 4, . . . , 9, the integer formed by the leftmost mdigits ofM is divisible by m.

Problem 2/36. The Fibonacci numbers are defined by F1 = F2 = 1 andFn = Fn1 + Fn2 for n > 2. It is wellknown that the sum of any 10consecutive Fibonacci numbers is divisible by 11. Determine the smallest

positive integer N so that the sum of any N consecutive Fibonacci numbersis divisible by 12.

Problem 3/36. Determine the value of

S =

1 + 112

+ 122

+

1 + 122

+ 132

+ +

1 + 119992

+ 120002

.

Problem 4/36. We will say

that an octogon is integral

if it is equiangular, its ver-

tices are lattice points (i.e.,

points with integer coordi-

nates), and its area is an in-

teger. For example, the fig-

ure on the right shows an

integral octogon of area 21.

Determine, with proof, the

smallest positive integer Kso that for every positive in-

teger k K, there is an in-tegral octogon of area k. x

y

1 2 3

123

Problem 5/36. Let P be a point interior to square ABCD so that P A =a ,PB = b,, P C = c, and c2 = a2 + 2b2. Given only the lengths a,b, and c,and using only a compass and straightedge, construct a square congruent to

square ABCD.


37/44


Problem 1/37. Determine the smallest five-digit positive integer N such that2N is also a five-digit integer and all ten digits from 0 to 9 are found in Nand 2N.

Problem 2/37. It was recently shown that 2224

+ 1 is not a prime number.Find the four rightmost digits of this number.

Problem 3/37. Determine the integers a,b,c,d, and e for which

(x2 + ax + b)(x3 + cx2 + dx + e) = x5 9x 27.

Problem 4/37. A sequence of real numbers s0, s1, s2, . . . has the propertythat

sisj = si+j + sij for all nonnegative integers i and j with i j,si = si+12 for all nonnegative integers i, ands0 > s1 > s2 > 0.

Find the three numbers s0, s1, and s2.

Problem 5/37. In the octahedron shown on

the right, the base and top faces are equilateral

triangles with sides measuring 9 and 5 units,and the lateral edges are all of length 6 units.

Determine the height of the octahedron; i.e.,

the distance between the base and the top face.

9 99

5

55

6

6

6

6

66


38/44


Problem 1/38. A well-known test for divis-

ibility by 19 is as follows: Remove the lastdigit of the number, add twice that digit to

the truncated number, and keep repeating this

procedure until a number less than 20 is ob-tained. Then, the original number is divisible

by 19 if and only if the final number is 19.The method is exemplified on the right; it is

easy to check that indeed 67944 is divisibleby 19, while 44976 is not.

6 7 9 4 /4

86 8 0 /2

4

6 8 /48

7 /61 2

1 9

4 4 9 7 /6

1 24 5 0 /9

1 8

4 6 /81 6

6 /24

1 0

Find and prove a similar test for divisibility by 29.

Problem 2/38. Compute 17761492!

(mod 2000); i.e., the remainder when17761492! is divided by 2000. (As usual, the exclamation point denotes fac-torial.)

Problem 3/38. Given the arithmetic progression of integers

308, 973, 1638, 2303, 2968, 3633, 4298,

determine the unique geometric progression of integers,

b1, b2, b3, b4, b5, b6,

so that

308 < b1 < 973 < b2 < 1638 < b3 < 2303 < b4 < 2968 < b5 < 3633 < b6 < 4298.

Problem 4/38. Prove that every polyhedron has two vertices at which the

same number of edges meet.

Problem 5/38. In ABC, segmentsPQ,RS, and T U are parallel to sidesAB,BC, and CA, respectively, and intersectat the points X,Y, and Z, as shown in the fig-ure on the right.

Determine the area ofABC if each of thesegments PQ,RS, and T U bisects (halves)the area of ABC, and if the area ofXY Z is one unit. Your answer should bein the form a + b

2, where a and b are posi-

tive integers. A U R B

P

X YQ

Z

S

T

C


39/44


Problem 1/39. Find the smallest positive integer with the property that it has

divisors ending in every decimal digit; i.e., divisors ending in 0, 1, 2, . . . , 9.

Problem 2/39. Assume that the irreducible fractions between 0 and 1, withdenominators at most 99, are listed in ascending order. Determine which twofractions are adjacent to 17

76in this listing.

Problem 3/39. Let p(x) = x5 + x2 + 1 have roots r1, r2, r3, r4, r5. Letq(x) = x2 2. Determine the product q(r1)q(r2)q(r3)q(r4)q(r5).

Problem 4/39. Assume that each member of the sequence < i >i=1 iseither a + or sign. Determine the appropriate sequence of+ and signsso that

2 =

6 1

6 2

6 3 .

Also determine what sequence of signs is necessary if the sixes in the nested

roots are replaced by sevens. List all integers that work in the place of the

sixes and the sequence of signs that are needed with them.

Problem 5/39. Three isosceles

right triangles are erected from the

larger side of a rectangle into the in-

terior of the rectangle, as shown onthe right, where M is the midpointof that side. Five circles are in-

scribed tangent to some of the sides

and to one another as shown. One

of the circles touches the vertex of

the largest triangle.

Find the ratios among the radii of

the five circles.

M


40/44


Problem 1/40. Determine all positive integers with the property that they

are one more than the sum of the squares of their digits in base 10.

Problem 2/40. Prove that ifn is an odd positive integer, then

N = 2269n + 1779n + 1730n 1776nis an integer multiple of2001.

Problem 3/40. The figure on the right can be divided into

two congruent halves that are related to each other by a glide

reflection, as shown below it. A glide reflection reflects a

figure about a line, but also moves the reflected figure in a

direction parallel to that line. For a square-grid figure, the

only lines of reflection that keep its reflection on the grid

are horizontal, vertical, 45 diagonal, and 135 diagonal. Ofthe two figures below, divide one figure into two congruent

halves related by a glide reflection, and tell why the other

figure cannot be divided like that.

Problem 4/40. Let A and B be points on a circle which are not diametricallyopposite, and let Cbe the midpoint of the smaller arc between A and B. LetD, Eand F be the points determined by the intersections of the tangent linesto the circle at A, B, and C. Prove that the area ofDEF is greater thanhalf of the area ofABC.

Problem 5/40. Hexagon RS T UV W isconstructed by starting with a right trian-

gle of legs measuring p and q, construct-

ing squares outwardly on the sides of thistriangle, and then connecting the outer

vertices of the squares, as shown in the

figure on the right.

Given thatp and q are integers withp > q,and that the area of RS T UV W is 1922,determine p and q. R S

T

U

V

W

q

p


41/44


Problem 1/41. Determine the unique positive two-digit integers m and n for

which the approximation

m

n = .2328767 is accurate to the seven decimals;i.e., 0.2328767 m/n < 0.2328768.

Problem 2/41. It is well known that there are infinitely many triples of

integers (a,b,c) whose greatest common divisor is 1 and which satisfy theequation a2 + b2 = c2.

Prove that there are also infinitely many triples of integers (r,s,t) whosegreatest common divisor is 1 and which satisfy the equation (rs)2 + (st)2 =(tr)2.

Problem 3/41. Supposecos3x

cos x =1

3 for some angle x, 0 x

2 . Deter-

minesin3x

sin xfor the same x.

Problem 4/41. The projective plane of order three consists of13 points and13 lines. These lines are not Euclidean straight lines; instead they are sets offour points with the properties that each pair of lines has exactly one point

in common and each pair of points has exactly one line that contains both

points. Suppose the points are labeled 1 through 13 and six of the lines areA = {1, 2, 4, 8}, B = {1, 3, 5, 9}, C = {2, 3, 6, 10}, D = {4, 5, 10, 11},E =

{4, 6, 9, 12

}, and F =

{5, 6, 8, 13

}. What is the line that contains 7 and

8?

Problem 5/41. In P QR,QR < P R < P Q sothat the exterior angle bisec-

tor through P intersects rayQR at point S, and the ex-terior angle bisector at R in-tersects ray

P Q at point T,

as shown on the right. Given

that P R = P S = RT, deter-

mine, with proof, the measureofP RQ.

P

Q T

R

S


42/44


Problem 1/42. How many positive five-digit integers are there consisting

of the digits 1, 2, 3, 4, 5, 6, 7, 8, 9, in which one digit appears once and twodigits appear twice? For example, 41174 is one such number, while 75355 isnot.

Problem 2/42. Determine, with proof, the positive integer whose square is

exactly equal to the number

1 +2001i=1

(4i 2)3.

Problem 3/42. Factor the expression

30(a2 + b2 + c2 + d2) + 68ab 75ac 156ad 61bc 100bd + 87cd.

Problem 4/42. Let X = (x1, x2, x3, x4, x5, x6, x7, x8, x9) be a 9-long vectorof integers. Determine X if the following seven vectors were all obtainedfrom X by deleting three of its components:

Y1 = (0, 0, 0, 1, 0, 1), Y2= (0, 0, 1, 1, 1, 0), Y3 = (0, 1, 0, 1, 0, 1),

Y4 = (1, 0, 0, 0, 1, 1), Y5= (1, 0, 1, 1, 1, 1), Y6 = (1, 1, 1, 1, 0, 1),

Y7

= (1, 1, 0, 1, 1, 0).

Problem 5/42. Let R and Sbe points on the sides BC and AC, respectively,ofABC, and let P be the intersection ofAR and BS. Determine the areaof ABC if the areas ofAP S, AP B, and BP R are 5, 6, and 7,respectively.


43/44


Problem 1/43. We will say that a rearrangement of the letters of a word has

no fixed letters if, when the rearrangement is placed directly below the word,

no column has the same letter repeated. For instance, the blocks of letters

below shows that E S A R E T is a rearrangement with no fixed letters ofT E R E S A, but R E A S T E is not.

T E R E S A T E R E S AE S A R E T R E A S T E

How many distinguishable rearrangements with no fixed letters does T E R E S Ahave? (The two Es are considered identical.)

Problem 2/43. Find five different sets of three positive integers {k,m,n},such that k < m < n and

1

k+

1

m+

1

n=

19

84.

Problem 3/43. Suppose p(x) = xn + an1xn1 + + a1x + a0 is a poly-

nomial with integer coefficients and suppose (p(x))2 is a polynomial all ofwhose coefficients are non-negative. Is it necessarily true that all the coeffi-

cients ofp(x) must be non-negative? Justify your answer.

Problem 4/43. As shown

in the figure on the right, in

ACF, B is the midpoint ofAC, D and Edivide side CFinto three equal parts, while

G, H and I divide side F Ainto four equal parts.

B

C

D

E

G H I AF

Seventeen segments are drawn to connect these six points to one another

and to the opposite vertices of the triangle. Determine the points interior to

ACFat which three or more of these line segments intersect one another.

Problem 5/43. Two perpendicular planes intersect a sphere in two circles.

These circles intersect in two points, spaced 14 units apart, measured along

the straight line connecting them. If the radii of the circles are 18 and 25

units, what is the radius of the sphere?


44/44


Problem 1/44. In a strange language there are only two letters, a and b, andit is postulated that the letter a is a word. Furthermore, all additional words

are formed according to the following rules:1. Given any word, a new word can be formed from it by adding a b at the

right hand end.

2. If in any word a sequence aaa appears, a new word can be formed byreplacing aaa by the letter b.

3. If in any word a sequence bbb appears, a new word can be formed byomitting bbb.

4. Given any word, a new word can be formed by writing down the se-

quence that constitutes the given word twice.

For example, by (4), aa is a word, and by (4) again, aaaa is a word. Henceby (2) ba is a word, and by (1), bab ia also a word. Again, by (1), babb isa word, and so by (4), babbbabb is also a word. Finally, by (3) we find thatbaabb is a word.

Prove that in this language baabaabaa is not a word.

Problem 2/44. Let f(x) = x x x x for all positive real numbers x,where y denotes the greatest integer less than or equal to y.

1. Determine x so that f(x) = 2001.

2. Prove that f(x) = 2002 has no solutions.

Problem 3/44. Let f be a function defined on the set of integers, and assumethat it satisfies the following properties:

1. f(0) = 0;2. f(1) = 3; and

3. f(x)f(y) = f(x + y) + f(x y) for all integers x and y.Determine f(7).

Problem 4/44. A certain company has a faulty telephone system that some-

times transposes a pair of adjacent digits when someone dials a three-digit

extension. Hence a call to x318 would ring at either x318, x138, or x381,while a call received at x044 would be intended for either x404 or x044.

Rather than replace the system, the company is adding a computer to de-duce which dialed extensions are in error and revert those numbers to their

correct form. They have to leave out several possible extensions for this to

work. What is the greatest number of three-digit extensions the company

can assign under this plan?

Problem 5/44 Determine the smallest number of squares into which one

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