A salesman sells goods by telephone. The probability that any particular call achieves a sale is, independently of all other calls. The salesman continues to make calls until one call achieves a sale.

(a) Name an appropriate distribution with which to model this situation.

(b) Calculate the probability that the call that achieves a sale (i) is the fifth call made, (ii) does not occur in the first five calls.

(c) Obtain the mean and variance of the number of calls the salesman makes. (C)