Math Divisibility Rules

Divisibility Rules

The divisibility rules make reducing fractions easier.

A number is divisible by 2 if it is an even number.

A number is divisible by 3 if the sum of the digits is divisible by 3.

A number is divisible by 4 if the last two digits are both zeros or if they are divisible by 4.

A number is divisible by 5 if it ends in 0 or 5.

A number is divisible by 6 if it is even and is divisible by 3.

A number is divisible by 9 if the sum of the digits is divisible by 9.

A number is divisible by 10 if it ends in 0.

A number is divisible y 7 if:

1. take last digit of number and double it
2. Subtract this number from the rest of the digits in the original #.
3. If this new number is either 0 or a number is divisible by 7.
   Example:
   1) The last digit of 203 is 3, double it is 3 x 2 = 6.
   2) Subtracting this new number, 6, from 20 ( the remaining digits of the origingal number 203) gives 14.
   3) Since 14 is divisible by 7, we can immediately tell that the original number, 203 is divisible by 7.

 A number is divisible by 8 if the last three digits are divisible by 8.