A self service store employs one cashier at its counter. Nine customers arrive on an average

every 5 mins while the cashier can serve 10 customers in 5 mins. Assuming Poisson

distribution for arrival and exponential distribution for service time, find

a) Average number of customer in system

b) Average number of customer in queue.

c) Average number of time spend in system

d) Average time a customer wait before being server.