I encountered this very elementary problem as I was practicing probability.
In a multiple-choice test, each question offers a choice of 5 answers, only one of which is correct. The probability that a student knows the correct answer is 5/8. If he does not know which answer is correct, he selects one of the 5 answers at random. Find the probability that he selects the correct answer to a question.
I'm having difficulties understanding where they received the denominator(8) from, shouldn't it be 1/5 ? Further what is the best way to tack this problem?