This question asks for the probability of the union of two events A ( pop) and B (had 500 - 1000 plays).
Since we know the probability of each event separately, P(A) = 0.9 and P(B) = 0.6, as well as the probability of their intersection, P(A ∩ B) = 0.5, the probability of their union is given by:
P(A U B) = P(A) + P(B) - P(A ∩ B) = 0.9 + 0.6 - 0.5 = 1
Therefore, the answer is 1.