Suppose that a certain college class contains 65 students. Of these, 35 are seniors, 33 are biology majors, and 5 are neither. A student is selected at random from the class.
(a) What is the probability that the student is both a senior and a biology major?
(b) Given that the student selected is a biology major, what is the probability that he is also a senior?
Write your responses as fractions.