Originally Posted by

**debaprosad** Thanks,

I am trying to solve the problem for several days, but for every efforts of mine end up with results nearby 18, so please guide me about how to solve the problem!!

Josh takes a twenty-question multiple-choice exam where each question has five possible answers. Some of the answers he knows, while others he gets right just by

making lucky guesses. Suppose that the conditional probability of his knowing the answer to a randomly selected question given that he got it right is 0.92. How many of the

twenty questions was he prepared for?