From a collection of 26 exercises, a student knows how to correctly solve 20 of them. If the teacher selects 8 exercises from the aforementioned collection to be the points for an evaluation exam. What is the probability that the exam has exactly 2 questions that the student does not know how to solve?

total number of ways of setting the paper = C(26, 8) = 1562275 Number of ways such that students gets exactly 6 known questions and exactly 2 unknown questions = C(20, 6) x C(6, 2) = 581400 Required probability $$ =\frac{581400}{1562275}\approx0.37215 $$