If 3∈A and 3B, then which of the following statements is not true?

A. 3 is an element of B complement.

B. 3 is an element of A∪B.

C. 3 is an element of A∩B.

This is how to answer the question:

If 3∉B it follows that 3∈B'; the complement is everything * not * in B. Our first statement is true.

Since 3∈A it follows that 3∈A∪B, since A⊆A∪B and therefore everything in A is also in A∪B. Statement 2 is also true.

Now, since A and B do not have 3 in common, it follows that 3∉A∩B. Hence statement 3 is not true.