Elementary Probability Question: Conditional case, with AT LEAST clause
Solution 1:
The question asks for the conditional probability that at least three shots were required to be shot. This means what is the chance that either three or four shots were fired and hit the plane, given that the plane was hit. This is just equal to the probability that it takes three or four shots, namely the 0.1176 that you calculated, divided by the probability that the gun hits the plane, 0.6976. When you divide the two, you'll notice that you get 0.1686.