Question

If A and B are subsets of the universal set X and n(X) = 50, n(A) = 35, n(B) = 20, n(A'∩ B') = 5, find: n(A ∪ B)

Answer 1

n(X) = 50, n(A) = 35, n(B) = 20, n(A'∩B') = 5

n (A∪B) = n(X) - [n(A ∪ B)']

= n(X) - n(A' ∩ B')

= 50 - 5

= 45