Unit 2 (5th Grade)

Unit 2

5th Grade

Unit Goals• Write and solve open sentences for number stori

es• Round numbers to designated places• Make magnitude estimates• Find the product of multi-digit whole numbers

and decimals• Identify the maximum, minimum, median, mode,

and mean for a data set (see data landmarks power point for more information)

Write and solve open sentences for number stories

• An open sentence is a number sentence or equation that contains a variable

I had three fish and bought some more at the pet store. After two died, I had eight fish left. How many fish did I buy?f = fish bought

3 + f – 2 = 8

1 + f = 8

f = 7

Define your variable (the quantity you don’t know)

Describe what took place using math operations

Combine like terms

Solve for the variable

Write and solve open sentences for number stories

It often helps to look for key words to help you decide what operations to use.

+ - X ÷ =increased bymore thancombined togethertotal ofsum

added to

decreased byminus

lessdifference between/ofless than

fewer than

oftimes

multiplied byproduct of

increased/decreased by afactor of

per

aout ofratio of quotient ofpercent

Is

Are

Was

Were

will begives yieldssold for

Try one!

Which open sentence describes the following number story?

Lucas was comparing prices on a pair of mini-speakers. At one store, the pair of speakers cost $19.95. At a second store, the same speakers cost $24.70. At a third store, they cost $18.50. If he buys the speakers at the lowest price, how much will he save over the highest price?

$24.70 + $19.95 = s

S= savings

$24.70 x $19.95 = s

S= savings

$24.70 - $19.95 = s

S= savings

$24.70 ÷ $19.95 = s

S= savings

Correct!

The correct open sentence is $24.70 - $19.95 = s because the phrase “save over the highest price” is asking you to find the DIFFERENCE (subtraction) between the highest and lowest prices.


Click here to return to the goals page

Keep Trying!

The correct open sentence is $24.70 - $19.95 = s because the phrase “save over the highest price” is asking you to find the DIFFERENCE (subtraction) between the highest and lowest prices.



Round numbers to designated places

• Remember place value!• Underline the value to which

you are rounding• Circle the digit to its right- this is

the number you will need to look at

• If the circled digit is 5 or more, change the underlined digit to the next highest number and make the rest of the digits to the right into zeros

• If the circled digit is 4 or less, leave the underlined digit alone and make the rest of the digits to the right into zeros


Round 1,342,365.1427 to the nearest thousand.

1. Underline the thousands place.2. Circle the hundreds place.3. The hundreds place is less than 54. Leave the 2 alone and change 3

and everything to the right of it into zeros

You are being asked to tell whether 1,342,365.1427 is closer to 1,342,000 or 1,343,000.

1,342,000.0000Try one on your own!


Round 234,567,890.0987 to the nearest million.

200,000,000

235,000,000

234,000,000

230,000,000

Correct!

The correct answer is 235,000,000.



Millions

Is 234,567,890.0987 closer to 234 million or 235 million?

234,567,890.0987

235,000,000

5 or more, round up!

Keep Trying!

The correct answer is 235,000,000.



Millions

Is 234,567,890.0987 closer to 234 million or 235 million?

234,567,890.0987

235,000,000

5 or more, round up!

Make magnitude estimates

• A magnitude estimate is a ballpark estimate of what your answer should be.

• It’s very helpful to use magnitude estimates to determine if your answer is reasonable.

1. Round the factors to the nearest multiple of 1038 is close to 4042 is close to 40

2. Find the product of the two rounded factors

40 x 40 = 1600

3. The answer should be in the 1000s

38 x 42 =1596

38 x 42 =

Make a magnitude estimate for 339 x 38= s.

Make magnitude estimates

300 x 40 = 12,000

The answer should be in the 10,000s

400 x 40 = 16,000

The answer should be in the 10,000s.

300 x 40 = 1,200


400 x 40 = 1,600


Correct!

The correct answer is 300 x 40 = 12,000… The answer should be in the 10,000s.


339 x 38 = 3 3 9 X 3 8________ 2 7 1 2 1 0 1 7 0________ 1 2, 8 8 2

Keep Trying!

The correct answer is 300 x 40 = 12,000… The answer should be in the 10,000s.


339 x 38 = 3 3 9 X 3 8________ 2 7 1 2 1 0 1 7 0________ 1 2, 8 8 2

Be sure to round to the

nearest multiple of 10- the number’s highest place

value!

339 is closest to 30038 is closest to 40300 x 40 = 12,000

.

Find the product of multi-digit whole numbers and decimals

• When multiplying multi-digit numbers, remember to keep place value lined up!

5 3 4 . 0

x 2 . 3

02251 Multiply 5340 x 3008601 Multiply 5340 x 20

020221 Add the productsMultiply by .01

Divide each number by .1


You can also multiply this way:5 3 4

x 2 3


28221 Add the products

0 0 0

0851 0 0

9 01 2

Multiply 20 x 4Multiply 3 x 500Multiply 3 x 30Multiply 3 x 4


A third way to multiply is:5 3 4

x 2 3


28221 Add the products

0 0 0

0851 0 0

9 01 2

Multiply 20 x 4Multiply 3 x 500Multiply 3 x 30Multiply 3 x 4

The Lattice Method

• Click here for a demonstration of the lattice method of multiplication.

• Another demonstration page


Use a method of multiplication to solve the following open number sentence:

43.25 x 36 = N

N = 15570

N = 125.7 N = 1557

N = 1257

Correct!

The correct answer is 43.25 x 36 = 1557.


43.25 x 36 = 4 3 . 2 5 X 3 6 . 0 0 ___________ 2 5 9 5 0 0 0 1 2 9 7 5 0 0 0 ___________ 1 5 5 7. 0 0 0 0

Keep Trying!

The correct answer is 43.25 x 36 = 1557.


43.25 x 36 = 4 3 . 2 5 X 3 6 . 0 0 ___________ 2 5 9 5 0 0 0 1 2 9 7 5 0 0 0 ___________ 1 5 5 7. 0 0 0 0

Technology

Unit 2 (5th Grade)