At a Midwestern university, 25% of the incoming freshmen drop out by their sophomore year. Suppose that a random sample of 200 incoming freshmen is selected. a. Find the probability that exactly 50 of them drop out by their sophomore year. (4 pts.) b. Find the probability that 50 or fewer of them drop out by their sophomore year. (5 pts.) c. Find the probability that at least 40 of them drop out by their sophomore year