Question

Which of the following numbers is not divisible by 3? a) 3,102 b) 236 c) 27 Which of the following numbers is divisible by 3? d) 4,518​

Answer 1

If the digits add to 3 or a multiple of 3, then the original number is a multiple of 3.

`3102 \to 3+1+0+2 = 6`

The sum 6 is a multiple of 3, which means 3102 is also a multiple of 3.

In contrast

`236 \to 2+3+6 = 11`

11 isn't a multiple of 3, which makes 236 not a multiple of 3 either.

27 is a multiple of 3 because 2+7 = 9 is a multiple of 3

4518 is also a multiple of 3 since 4+5+1+8 = 18 is a multiple of 3.

Summary

`\begin{array}c \cline{1-2}\text{Multiple of 3} & \text{Not multiple of 3}\\\text{3102 and 27 and 4518} & 236\\\cline{1-2}\end{array}`