DIVISIBILITY RULE FOR 3 AND 6

Is it multiple of 3?

Can you divide it by 3?

The divisibility for rule for three is really useful to know.

A number is divisible by 3 if the sum of each digit is either 3, 6 or 9.

With it you can very quickly know if a number is a multiple of three. 

For example;

51            Add the two digits                 5 + 1 = 6

                The answer is 6 so therefore 51 is a multiple of 3

109          Add the three digits         1 + 0 + 9 = 10     now add 1 + 0 = 1

                  The answer is not a 3, 6 or 9 so 109 is not divisible by 3

4125        Add the digits       4 + 1 + 2 + 5 = 12

                Add the digits        1 + 2 = 3

                   4125 is a multiple of 3

2715219        Add the digits 2 + 7 + 1 + 5 + 2 + 1 = 18                     Add 1 + 8 = 9

                        2715219 is divisible by 3

Knowing this rule is also useful for identifying numbers that are multiples of 6.

The divisibility rule for 6 is that the number has to be even and the sum of the digits are divisible by 3.

For example:

72    Add the digits together 7 + 2 = 9

        72 is a multiple of 6. 

It is an even number and the sum of the digits is 9 and therefore a multiple of 3.

93    Add the digits together        9 + 3 = 12        1 + 2 = 3

Although 93 is divisible by 3 it is not divisible by 6 because it is an odd number.

My students really enjoy experimenting with numbers to see if they are multiples of 3 or divisible by 6.  They especially enjoy creating small presentations to show others their maths skills.