Suppose that 50 lottery tickets are sold. Among them, 20 tickets pay off at lest the cost of the ticket. Now, suppose that you buy five tickets. What is the probability that you will win back at least the cost of four tickets?

For the answer, professor put that Pr(X=4) but shouldn't it be Pr(X \geq4)? Maybe I'm just missing something?

Hmm.. Upon reading it again, the problem asks what the probability is that you will win back at least the cost of four tickets. I was thinking that it said what is the probability that you will win back the cost of at least four tickets.

It's funny how the placement of one word can totally change a problem.