The Northern Emergency Computer Support has a call center with 10 customer service representatives. Historical statistics show that the durations of customer calls are exponentially distributed, and the average call duration is 20 minutes. Customer calls arrive according to a Poisson process. The arrival rate is 15 customer calls per hour (on average). Use approximation formulas for your calculation.
How long, on average, does a customer have to wait (before a representative picks up his or her call)?