# 2 - Divisibility rules

## Whole numbers

A whole number is a number which does not have a decimal point :

4 is a whole number
3,7 is not a whole number
- 100 is a whole number
0,01 is not a whole number.

## Divisibility of a number by another number

We say that a number is divisible by another number if the result of their division is a whole number.

12 is divisible by 2 because .
11 is not divisible by 3 because .
5 is not divisible by 2 because .
3123 is divisible by 9 because
125 is divisible by 5 because .
93 is not divisible by 5 because .

## Divisibility rules

A number is divisible by 2 if it ends with 0, 2, 4, 6, ou 8.
A number is divisible by 3 if the sum of its figures is divisible by 3.
A number is divisible by 5 if it ends with 0 or 5.
A number is divisible by 9 if the sum of its figures is divisible by 9.

Examples :

The number 309 is divisible by 3 because the sum of its figures is 12 and 12 is divisible by 3 ( ).
The number 1997 is not divisible by 9 because the sum of its figures is 26 and 26 is not divisible by 9 ( ).
The number 44 is not divisible by 5 because it does not end with either 0 or 5.
The number 123456 is divisible by 2 because it ends with 6.

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