Question

What is the test of divisibility of 18?

Answer 1

Explain the test of divisibility of $18$.

A number divisible by $18$ must also be divisible by $2$ and $9$.
The converse is also true: a number divisible by $2$ and $9$ must also be divisible by $18$.
So, test for divisibility by $2$ and $9$.
1. If the number is divisible by two, the last digit of a number must be even.
2. If the number is divisible by $9$, the sum of all the digits of a number must be a multiple of $9$.

Hence, if a number passes both of these criteria, it is almost certainly divisible by $18$.

Example: Assume the number $792$ which is an even number.

So, it is divisible by $2$.

Also, $7+9+2=18$ is divisible by $9$.

Hence, the number $792$ is divisible by $18$.