Event A and B are disjointed. Pr[A] = 0.15, Pr[B] = 0.45. Find Pr[A U B']

Answer 1

If A and B are disjoint, AB = ∅, so A U B' = AB ∪ AB' ∪ A'B' = ∅ ∪ AB' ∪ A'B' = B'

As P(B) = .45, P(B') = 1 - .45 = .55.

Thus, P(A U B') = .55