申論題

5.

(2). Seventy-five percent of the graduates of a driver training school pass the official driver's test on the first attempt, and the other 25 percent fail. The school gives a pretest to graduates before they take the official test. Of the graduates who pass the official test on the first attempt, 90% passed the pretest. Of the graduates who fail the official test on the first attempt, 20% passed the pretest.
We wish to know the probability that a graduate can pass the official test on the first attempt, given that he passed the school pretest. (6%)