Need answer only for question# 8

Q7. Customers arrive at a rate of 180 per hour at either of two vending machines, each of which can

service 240 customers per hour. Assuming a Poisson distribution for arrivals and an exponential

distribution for the service time, determine the expected waiting time per customer. Recalculate if one

of the vending machines is broken and cannot be used.

Q8. In Question 7 above, if the cost of operating a vending machine over its lifetime is $100 per day,

and the cost of having customers waiting for service is 50 cents per minute, what is the optimum

number of vending machines?