Question

Which of the following is not an element of the following set:
A: {positive integers divisible by 3}

3

21

14

30

Answer 1

In order to be an element of set A, the element must be
(1) A positive integer
and
(2) Divisible by 3

They're all positive integers, so just figure out which one is not divisible by 3. If it's not divisible by 3, then by definition, it is not a part of set A.