Customers checking out at Food Tiger arrive in a single-line queue served by two cashiers at a rate of eight per hour according to a Poisson distribution. Each cashier processes customers at a rate of eight per hour according to an exponential distribution.
a. If, on average, customers spend 30 minutes shopping before getting in the checkout line, what is the average time a customer spends in the store?
b. What is the average number of customers waiting for service in the checkout line?
c. What is the probability that a customer must wait?
d. What assumption did you make to answer this question?