Divisibility Rules Divisibility Rules

Section 4-1Section 4-1

Bell Ringer #1Bell Ringer #1

►Go to page 152 in your books and Go to page 152 in your books and copy the chart of divisibility rules into copy the chart of divisibility rules into your notebook. This is a requirement your notebook. This is a requirement for your next notebook check so for your next notebook check so please do not lose this page. please do not lose this page.

The # 2The # 2

►Checking if a number is divisible by 2 Checking if a number is divisible by 2 is the easiest one. If the number ends is the easiest one. If the number ends in an even number (0 , 2, 4, 6, 8) then in an even number (0 , 2, 4, 6, 8) then the number is divisible by 2. the number is divisible by 2.

►Examples: 120, 68, 146, 12 are all Examples: 120, 68, 146, 12 are all divisible by 2. divisible by 2.

The # 3The # 3

►This one can be tricky. For the #3, you This one can be tricky. For the #3, you must ADD all the digits together and must ADD all the digits together and see if that number is divisible by 3. see if that number is divisible by 3.

►Example: 423 = 4+2+3=9Example: 423 = 4+2+3=9►9 is divisible by 3 so 423 is divisible by 9 is divisible by 3 so 423 is divisible by

3. 3.

#4#4

►For 4, look at the last 2 digits of a For 4, look at the last 2 digits of a number. If those two digits form a number. If those two digits form a number that is divisible by 4, then the number that is divisible by 4, then the whole number is divisible by 4. whole number is divisible by 4.

►Example: 632…..the last two numbers Example: 632…..the last two numbers are 32. Since 32 is divisible by 4, 632 are 32. Since 32 is divisible by 4, 632 is divisible by 4. is divisible by 4.

#5#5

►5 is another easy one. If a number 5 is another easy one. If a number ends in a 0 or a 5, then the number is ends in a 0 or a 5, then the number is divisible by 5.divisible by 5.

►Example: 215, 420, 830. Example: 215, 420, 830.

#6#6

► For 6, you must check the divisibility for 2 For 6, you must check the divisibility for 2 and 3 first. If the number is divisible by both and 3 first. If the number is divisible by both of them, then it is also divisible by 6. of them, then it is also divisible by 6.

► Example: 192Example: 192► Check 2: ends in a 2 Check 2: ends in a 2 ► Check 3: 1 + 9 + 2 = 12 which is divisible Check 3: 1 + 9 + 2 = 12 which is divisible

by 3.by 3.► So the whole number 192 is divisible by 6. So the whole number 192 is divisible by 6.

#9#9

►The same rule that applied to 3 applies to The same rule that applied to 3 applies to 9 as well. You must add all the digits 9 as well. You must add all the digits together and see if that number is together and see if that number is divisible by 9. divisible by 9.

►Example: 5931= 5 + 9 + 3 + 1 = 18Example: 5931= 5 + 9 + 3 + 1 = 18►18 is divisible by 9 so 5,931 is divisible by 18 is divisible by 9 so 5,931 is divisible by

9. 9.

#10#10

► If the number ends in a 0, it is divisible If the number ends in a 0, it is divisible by 10. by 10.

►Examples: 210, 150, 10, 40. Examples: 210, 150, 10, 40.

ExampleExample

►Check if the number 610 is divisible by Check if the number 610 is divisible by 2,3,4, and 5. 2,3,4, and 5.

►2: ends in a 0 so ___________2: ends in a 0 so ___________►3: 6 + 1 + 0 = 7 so __________3: 6 + 1 + 0 = 7 so __________►4: 1 + 0 = 1 so ____________4: 1 + 0 = 1 so ____________►5: ends in a 0 so _____________5: ends in a 0 so _____________►So 610 is divisible by ___________So 610 is divisible by ___________

Prime and Composite #’sPrime and Composite #’s

►This is a topic that will be confusing at This is a topic that will be confusing at first, but once you understand first, but once you understand divisibility, it will become easier. divisibility, it will become easier.

Prime and Composite #’sPrime and Composite #’s

►Prime Number: A number that is Prime Number: A number that is divisible ONLY by 1 and itself. divisible ONLY by 1 and itself.

►Examples: 2, 3, and 5 are only Examples: 2, 3, and 5 are only divisible by 1 and themselves. divisible by 1 and themselves.

►Composite Number: Any number that Composite Number: Any number that isn’t a prime number. (divisible by isn’t a prime number. (divisible by more than two numbers) more than two numbers)

Examples:Examples:

►Tell whether each number is prime or Tell whether each number is prime or composite. If composite, list what it is composite. If composite, list what it is divisible by. divisible by.

►45:____________45:____________►13:____________13:____________►19:____________19:____________►49:____________49:____________

Lesson QuizLesson Quiz

►1) Tell whether 462 is divisible by 2, 3, 1) Tell whether 462 is divisible by 2, 3, 4, and 5.4, and 5.

►2) Prime or Composite2) Prime or Composite►2323►4848►3131►1818►