Let A and B be subsets of a universal set U and suppose n(U) = 350, n(A) = 130, n(B) = 90, and n(A B) = 50.

Question

Find the number of elements in the set.
n(Ac n B)

Answer 1

Sketch out the Venn Diagram.
You are looking for where everything outside of A connects with B.
So that is the stuff in B, that is not also in A
There is 90 total in B.
But you need to remove the 50 that are in both A and B.
That will give you your answer : )

Answer 2

So multiple 130 with 90 and 350?