A ∩ B = ∅. P(B) = .9 P(A ∪ B) = .9. Find P(A).

Given:  P(A ∩ B) = 0, P(B) = 0.9, P(A ∪ B) = 0.9.

We have: P(A ∪ B) = P(A) + P(B) - P(A ∩ B)

=>  0.9 = P(A) + 0.9 - 0

=> P(A) = 0.9 - 0.9 = 0

Hope this helps!

:)