Assume the probability that you will make a sale on any given telephone call is 0.24. Find the probability that you make your first sale on the fifth call, make your sale on the first, second or third call, and you do not make a sale on the first three calls.

Question

Assume the probability that you will make a sale on any given telephone call is 0.24.  Find the probability that you make your first sale on the fifth call, make your sale on the first, second or third call, and you do not make a sale on the first three calls.

cwrw238 · Answer

the probabilities of each sale are independent of any previous calls so you multiply the probabilities.

for the first part (first sale on 5th call) the required probability is

P(no sale)^4 * p(sale)
= (1 - 0.24)^4 * 0.24


the other parts are worked out in a similar way.