National Bank is considering opening a drive-through window for customer service. Management estimates that customers will arrive at the rate of 10 per hour. The teller who will staff the window can serve customers at the rate of one every four minutes. Assuming Poisson arrivals and exponential service. Because of limited space availability and a desire to provide an acceptable service level for the system, the bank manager would like to consider the following:
a) What is the present service level for the two, three, four cars limit?
b) What must be the service rate to assure 95 % level of service with three cars limit?