[BruceZ]

Bayes' theorem problem. Hornblower lives 60% of the time, and his opponent draws the shot 50% of the time. The probability Hornblower drew the shot given that he lived is 50%/60% = 5/6, so the probability his opponent drew the shot is 1/6.

Here's another way.
P(opponent has shot GIVEN hornblower lives) = P(opponent has shot AND hornblower lives)/P(hornblower lives) = (.5)(.2)/.6 = 1/6.