1) In a waiting line system, there is only one server. Customer arrivals follow Poisson distribution with mean inter-arrival time 5 minutes.

1) In a waiting line system, there is only one server. Customer arrivals follow Poisson distribution with mean inter-arrival time 5 minutes. Service time follow exponential distribution and a server can serve 15 customers per hour on average. What is the average waiting time?

a)2 min

b)none of the answer

c)20 min

d)30 min

e)16 min