Assume the probability that you will make a sale on any given telephone call is 0.13. find the probability that you (a) make your first sale on the fifth call, (b) make your sale on the first, second, or third call, and (c) do not make a sale on the first three calls.

We are given that  the probability that you will make a sale on any given telephone call is 0.13.

Probability of success i.e. sale = p = 0.13

Probability of failure i.e. no sale = q = 1-0.13=0.87

(a) make your first sale on the fifth call

We will use geometric distribution

The geometric distribution is a discrete distribution for n=0, 1, 2, ... having probability density function

sale is made on 5 th call

So. substitute n = 5

The probability that you make your first sale on the fifth call is 0.0744

b)make your sale on the first, second, or third call

The probability that you make your sale on the first, second, or third call is 0.3414

(c) do not make a sale on the first three calls.

Using part b

The probability that you do not make a sale on the first three calls is

0.6586