# A discrete mathematics problem by Akshit Kumar

**Discrete Mathematics**Level 3

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 \(a+b\).