# A discrete mathematics problem by Akshit Kumar

In an entrance test there are multiple choice questions. There are four possible answers to each question of which exactly one option is correct. The probability that a student knows the answer to a question is 90 %. If he does not know the answer, he guesses randomly. Given that he gets the correct answer to a question, then the probability that he was guessing is $$\frac{a}{b}$$, where and b are co-prime integers. Find $$a+b$$.

×