If n(A - B) = 15, n(B - A) = 10, and n(A ∩ B) = 5, find n(A ∪ B).
Answer: C
The union of two sets can be visualized as the sum of three disjoint regions: elements only in A, elements only in B, and elements in both.
n(A ∪ B) = n(A - B) + n(B - A) + n(A ∩ B)
Substituting the given values:
n(A ∪ B) = 15 + 10 + 5 = 30.