Then compute the probability of B in each situation (these are the P(B|An)). Finally weigh each of these probabilities with the probabilities that you are in the An situation (these are the P(An)"s). Example: Cards are drawn one by one from a standard 52-card deck without replacement. What is the probability that the third spade is drawn on the 8th draw? Example: (Problem 4.27, page 144) Students are given three chances to pass a basic skills exam for permission to enroll in Calculus I. Sixty percent of the students pass on the first try; of those who fail on the first try, 54% pass on the second try; and, of those remaining, 48% pass on the third try. What percentage of students pass?