In a survey of undergraduate library usage, it was found that 78% of seniors, 65% of juniors, 41% of sophomores, and 21% of freshmen use the library frequently. Suppose that 15% of the undergraduates are seniors while the corresponding percentages for juniors, sophomores, and freshmen are 20%, 25%, and 40% respectively.
What percent of the students use the library frequently?
Suppose you see a student use the library everyday. What is the probability that this student is a freshman?