Suppose that in one of your classes you are given 20 questions, and are told that the final exam will consist of 8 of them. Suppose that the 8 that are chosen for the final are selected randomly.
a) If you work out how to do 12 of the problems, what is the probability that you will be able to work at least 7 of those on the final?
b) How many problems do you need to have worked out to have a 90% probability of being able to solve all 8 of those on the final?
