380.Did Gabe Know It?
★★★conditional probabilityCh. 2 — Axiomatic and Conditional Probability444+ Problems in Probability
On a multiple-choice exam with 5 options per question, Gabe either knows the answer (and answers correctly) or guesses uniformly at random. The probability he knows the answer to any question is . Given that an answer was correct, find the probability that he knew it.
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Bayes: compare the two ways an answer ends up correct.
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