Question

What is the test of divisibility of 18?

Answer 1

A number that is divisible by 18 must be divisible by both 2 and 9.

The inverse is also true:
A number that is divisible by both 2 and 9 must be divisible by 18.

Therefore, we just have to test for both divisibility by 2 and 9.

• If a number is divisible by 2, its last digit must be even.
• If a number is divisible by 9, the sum of all its digits must be a multiple of 9

If a number passes both tests, then it will surely be divisible by 18.

Answer 2

Test of divisibility of `18` is that units digit is even i.e. it is either `0,2,4,6` or `8` and simultaneously sum of the digits is divisible by `9`.

Explanation:

Factors of `18` are `2` and `9` and hence divisibility by `18` means divisibility both by `2` and `9`.

Divisibility test of `2` being that units digit is divisible by `2` i.e. it is either `0,2,4,6` or `8`.

Divisibility test of `9` is that sum of all the digits is divisible by `9`.

Hence test of divisibility of `18` is that units digit is even i.e. it is either `0,2,4,6` or `8` and simultaneously sum of the digits is divisible by `9`.