Instead of actually carrying out a division, it is possible to "test" a number to see if it can be divided exactly by certain numbers.

If a number divides exactly into a number, it is divisible by this number.

24 is divisible by 2, because 24 ÷ 2 is a whole number.

24 is not divisible by 5, because 24 ÷ 5 is not a whole number.

Here are the rules to test divisibility by 2, 3, 4, 5, 6, 8, 9 and 10.

__Rule for 2__

A number is divisible by 2 if it ends in 0, 2, 4, 6 or 8.

This means that it is even.

__Rule for 3__

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

3045 is divisible by 3, because 3 + 0 + 4 + 5 = 12 which is divisible by 3

3044 is therefore not divisible by 3, because 11 is not divisible by 3.

**Rule for 4
**

A number is divisible by 4 if the number formed by its last two digits is divisible by 4.

3140 is divisible by 4, because 40 is divisible by 4.

3145 is not divisible by 4, because 45 is not divisible by 4.

**Rule for 5**

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

3045 is divisible by 5, because it ends in 5.

3030 is divisible by 5, because it ends in 0.

5551 is not divisible by 5.

__Rule for 6
__

**Both **the rules for 2 and 3 must work

**Rule for 8
**

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

3240 is divisible by 8, because 240 is divisible by 8.

3145 is not divisible by 8, because 145 is not divisible by 8.

**Rule for 9
**

This is similar to the rule for 3.

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

7065 is divisible by 9, because 7 + 0 + 6 + 5 = 18 which is divisible by 9

3045 is therefore not divisible by 9, because 12 is not divisible by 9.

**Rule for 10**

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

3140 is divisible by 10, because it ends in 0.

3145 is not divisible by 10.

**Rule for 11**

A number is divisible by 11 if alternate digit sums differ by 0 or a multiple of 11

**Example**

Is 3813 divisible by 6?

**Answer**

No, because 3 + 8 + 1 + 3 = 15, which is divisible by 3, but it is not divisible by 2 as it ends in a 3 which is odd.

**Example**

Is 2153864 divisible by 4?

**Answer**

Yes, because 64 is divisible by 4.

**Example**

Is 17226 divisible by 11?

**Answer**

Underline alternate numbers to get __1__7__2__2__6__

Add up the underlined digits to get the sum of 1 + 2 + 6 = 9

Add up the non-underlined digits to get the sum of 7 + 2 = 9

These two digit sums are equal or differ by a multiple of 11, so 17226 is divisible by 11.