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# Math 8 presentation: Divisibility rules

Divisibility rules for 10, 9, 5 and 7
by

## Kaeley Holbrook

on 13 December 2012

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#### Transcript of Math 8 presentation: Divisibility rules

Divisibility Rules Divisibility Rule for 10 The divisibility rule for 10 is quite simple. All you have to do is look at the last digit to see if it is a 0. if the last digit is not a 0 it will not be divisible by 10.
For example: 320 is divisible by 10 because the last digit is 0, 457 on the other hand is not divisible by 10 because the last digit is 7 not 0. Divisibility rule for 9 The divisibility rule for 9 is simple. If you add all the digits up and they equal 9 or any other number that equals 9 it is divisible by 9.
For example: 27, 2+7=9 so 27 is divisible by 9.
288, 2+8+8=18 and 1+8=9 so 288 is divisible by 9. Divisibility rule for 5 The divisibility rule for 5 is almost as easy as 10. If the last digit is 5 or 0 it is divisible by 5.
For example: 22, the last digit is 2 so it is not divisible by 5
40, the last digit is 0 so it is divisible by 5 Divisibility rule for 7 The divisibility rule for 7 is definitely the hardest of all that I have shown you. To find out if a number is divisible by 7 you must double the last digit, then subtract it from the remaining digits of the number. If the answer is divisible by 7 then the original number also will be.
For example: 616, 6x2=12, 61-12=49 and 49 is divisible by 7, therefore 616 is divisible by 7 It is easy to check if a number is divisible by 10. How many other "tests of divisibility" can you find? divisibility by 5, 7 or 9? Divisibility rule for 1 The divisibility rule for 1 is simple because all
numbers are divisible by 1. Divisibility rule for 2 Any even number is divisible by
2.
For example, 368 is divisible by
2 because 8 is and even number. Divisibility rule for 3 A number is divisible by 3 if the
sum of the digits is a number
divisible by 3.
For example, 468, 4+6+8= 18 &
18 is divisible by 3. Divisibility rule for 4 A number is divisible by 4 if the
last 2 digits are divisible by 4.
For example, 112, 12 is divisible
by 4 so 112 is divisible by 4. Divisibility rule for 6 You know a number is divisible by 6 if you
combine the rules for 2 and 3.
For example, 12 is divisible by 6 because it
passes the rules for both 2 and 3. Divisibility rule for 8 A number is divisible by 8 if the last 3
digits are divisible by 8.
For example, 9640 is divisible by 8 because
640/8=80 Divisibility rule for 11 To determine if a number is divisible by 11 you must alternately add & subtract the digits from left to right.
For example: 726 is divisible by 11 because, 7-2+6=11 Divisibility rule for 12 To see if a number is divisible by 12 it must pass the rules for both 2 and 3. Divisibility rule for 13 To check if a number is divisible by thirteen you must add 4 times the last digit to the rest.
For example: 637, 63+7x4=91, 9+1x4=13
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