question_answer 35)

In answering a question on a multiple choice test, a student either knows answer or guesses. Let  be he probability that he knows the answer and be the probability that he guesses. Assuming that a student wo guesses at the answer wi be correct with probability  What is the probability that the student knows the answer given that the answered it correctly ?  

Answer:

Let E1 and E2 are the events that the student knows the answer and the student guesses respectively.       Let A = event that the student answers correctly.             Required probability = P(E1/A)