A manufacturing firm just received a shipment of 20 assembly parts, of slightly varied sizes, from a vendor. The manager knows that there are only 15 parts in the shipment that would be suitable. He examines these parts one at a time.
a. Find the probability that the first part is suitable.
b. If the first part is suitable, find the probability that the second part is also suitable.
c. If the first part is suitable, find the probability that the second part is not suitable.