If a universal set contains 250 elements, n(A) = 90, n(B) = 125, and n(A ∩ B) = 35, find n(A ∪ B)'.

If a universal set contains 250 elements, n(A) = 90, n(B) = 125, and n(A ∩ B) = 35, find n(A ∪ B)'.

We know from set theory that:
n(A U B) = n(A) + n(B) - n(A ∩ B)

Plugging in our given values, we get:
n(A U B) = 90 + 125 - 35
n(A U B) = 180

The problem asks for n(A U B)'. This formula is found with:
n(A U B)' = n(U) - n(A U B)

n(U) is the universal set which is 250, so we have:
n(A U B)' = 250 - 180
n(A U B)' = 70