1. Divisibility Rules
Section 4-1

2. Bell Ringer #1
Go to page 152 in your books and copy the chart of divisibility rules into your notebook. This is a requirement for your next notebook check so please do not lose this page.

3. The # 2
Checking if a number is divisible by 2 is the easiest one. If the number ends in an even number (0 , 2, 4, 6, 8) then the number is divisible by 2.
Examples: 120, 68, 146, 12 are all divisible by 2.

4. The # 3
This one can be tricky. For the #3, you must ADD all the digits together and see if that number is divisible by 3.
Example: 423 = 4+2+3=9
9 is divisible by 3 so 423 is divisible by 3.

5. #4
For 4, look at the last 2 digits of a number. If those two digits form a number that is divisible by 4, then the whole number is divisible by 4.
Example: 632…..the last two numbers are 32. Since 32 is divisible by 4, 632 is divisible by 4.

6. #5
5 is another easy one. If a number ends in a 0 or a 5, then the number is divisible by 5.
Example: 215, 420, 830.

7. #6
For 6, you must check the divisibility for 2 and 3 first. If the number is divisible by both of them, then it is also divisible by 6.
Example: 192
Check 2: ends in a 2
Check 3: = 12 which is divisible by 3.
So the whole number 192 is divisible by 6.

8. #9
The same rule that applied to 3 applies to 9 as well. You must add all the digits together and see if that number is divisible by 9.
Example: 5931= = 18
18 is divisible by 9 so 5,931 is divisible by 9.

9. #10 If the number ends in a 0, it is divisible by 10.
Examples: 210, 150, 10, 40.

10. Example Check if the number 610 is divisible by 2,3,4, and 5.
2: ends in a 0 so ___________
3: = 7 so __________
4: = 1 so ____________
5: ends in a 0 so _____________
So 610 is divisible by ___________

11. Prime and Composite #’s
This is a topic that will be confusing at first, but once you understand divisibility, it will become easier.

12. Prime and Composite #’s
Prime Number: A number that is divisible ONLY by 1 and itself.
Examples: 2, 3, and 5 are only divisible by 1 and themselves.
Composite Number: Any number that isn’t a prime number. (divisible by more than two numbers)

13. Examples:
Tell whether each number is prime or composite. If composite, list what it is divisible by.
45:____________
13:____________
19:____________
49:____________

14. Lesson Quiz 1) Tell whether 462 is divisible by 2, 3, 4, and 5.
2) Prime or Composite 23 48 31 18