Tuesday, August 28, 2012

Divisibility Rules


Divisible by 2:  All even numbers (2,4,6,8...).

Divisible by 3:  Add all of the digits in the number; if the sum is divisible by 3, then so is the number.  For example, to find out if 255 is a multiple of 3, add its digits.  2+5+5=12 since 12 is divisible by 3, so is 255.

Divisible by 4: If the last two digits are a number that is divisible by 4, so is the original number.  For example, in the number 3,816 the last two digits of the number is 16, which is divisible by 4, so 3,816 is also divisible by 4.

Divisible by 5: All numbers ending in 5 or 0.

Divisible by 6: If the number is divisible by 2 or 3, it is also divisible by 6.

Divisible by 7: Take the last digit of the number and multiply it by 2.  Subtract that number from the other digits of the number aside from the last digit.  For example, 357, take 7, which is the last digit of the number, and multiply it by 2.  7(2)=14  Next, subtract this number from the the other digits other than the last digit, which is 35.  35-14=21  21 is divisible by 7, so that means 357 is divisible by 7, too.

Divisible by 8: If the last three digits of the number is divisible by 8, then is the number, too.  For example, 6, 056, since the last three digits are divisible by 8, so is 6,056.

Divisible by 9: Add up all the digits in the number; if the sum is divisible by 9, so is the number.  For example, to find out if 765 is divisible by 9, add the digits.  7+6+5=18 since 18 is divisible by 9, so is 765.

Divisible by 10: If the number ends in 0, then it is divisible by 10.

I hope this helps you!

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