Good customer service is always one of the key successes to a company. Anelectricity company aims to keep the customers waiting time on the phone to be less than12 minutes. Let X (in minutes) be the waiting time of a customers call to the CustomerService Call Centre. According to past records, the waiting time can be assumed tofollow an exponential distribution with a mean of 4 minutes, i.e. X ~ Exp( = 0.25).

If 100 calls are randomly selected, find the probability that the average waiting time is less than 4.6 minutes.