You may consider A and B as the subsets of the universal set U. Then (A ∩ B') = A \ (A ∩ B). ( Elements of A that are not in B ) The sign " \ " means subtraction of sets ) Therefore, you need first to find P(A ∩ B) and then subtract it from P(A). Step 1. P((A ∩ B) = P(A) + P(B) - P(AUB) =+ - = = . Step 2. P(A ∩ B') = P(A \ (A ∩ B)) = P(A) - P((A ∩ B) = - = - = = . Answer. P(A ∩ B') =