The call center serves callers with a Poisson distribution at the rate of 9 per hour. Service takes an average of 6 minutes and the service times can be considered to follow an exponential distribution.
What is the (a) minimum number of servers required so that at least 70% of the callers can receive service immediately?
(b) minimum number of severs required so that the average time a caller waits for service is no more than 30 minutes as advertised? No more than 15 minutes?