The student took the exam after learning 60 of the 75 questions. He was asked three questions. What is the probability that

he

(a) was able to answer two questions

(b) was able to answer at least one question.

For both (a) and (b):

a) Record the event for which the probability is requested using the symbols provided.

b) Provide a calculation formula and make sure that the preconditions for using the formula are met.

c) Calculate the requested probability. (Convert details and calculations in detail.)