The probability that you will make a sale on any

The probability that you will make a sale on any given telephone call is 0.19. Find the probability that you
(a) Make your first sale on the fifth call,
(b) Make your first sale on the first, second, or third call,
(c) Do not make a sale on the first three calls.
Find the indicated probabilities using the geometric distribution, the Poisson distribution, or the binomial distribution. Then determine whether the events are unusual. If convenient, use a table or technology to find the probabilities.