Problem: Suppose that a customer calls a call-center every minute on average and an agent can help a customer in 3 minutes on average. Both the time between customer calls and the time it takes an agent to help a customer are exponentially distributed.
a) What is the minimum number of agents needed so that the call-center is a feasible system?
b) Suppose that there are 5 agents. What is the percentage of customers, who does not have to wait in line until an agent starts helping them?
c) As a customer, when you call this call center (with 5 agents), what is the probability that there are exactly three customers waiting in front of you for an agent?
d) With 5 agents, what is the percentage of customers, who wait for an agent more than the average time it takes to reach to an agent?