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Divisibility Rules

Divisibility Rules. Section 4-1. 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. The # 2.

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Divisibility Rules

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  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: 1 + 9 + 2 = 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= 5 + 9 + 3 + 1 = 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: 6 + 1 + 0 = 7 so __________ • 4: 1 + 0 = 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

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