Question: A person enters a bank and finds all of the four clerks busy serving customers. There are no other customers in the bank, so the person will start service as soon as one of the customers in service leaves. Customers have independent, identical, exponential distribution of service time.
(a) What is the probability that the person will be the last to leave the bank assuming that no other customers arrive?
(b) If the average service time is I minute, what is the average time the person will spend in the bank?
(c) Will the answer in part (a) change if there are some additional customers waiting in a common queue and customers begin service in the order of their arrival?