Customers arrive, on average, at the rate of two per minute at a bank in downtown Portland.

(a) Define an appropriate probability model for the experiment of observing the number of customers entering the bank in a 5-minute period.

(b) What is the probability that there will be more than 20 customers entering the bank in a 5 -minute period?

(c) What is the expected number of customers that will enter the bank during a 5 -minute period?

(d) If the bank staff can service a maximum of 20 customers in a 5-minute interval, what is the probability that the customer load will exceed capacity in a 5 -minute interval, so that some customers will experience delays in obtaining service?