A student prepares for an exam by studying a list of 12 problems. She can solve 9 of them. For the exam, the instructor selects 7 problems at random from the 12 on the list given to the students. What is the probability that the student can solve 5 of the 7 problems on the exam?
I am really confused by this problem. My first initial thought was to do:
(5 chose 7)(7 chose 0)/ (12 chose 7)
I am not 100% sure about this though.