Automobiles arrive at the drive-thru window at the downtown Baton Rouge, Louisiana post office at the rate of 4 every 10 minutes. The average service time is 1.5 minutes. The Poisson distribution is appropriate for the arrival rate and service times are exponentially distributed.
a) What is the probability that there are exactly 2 cars in the system?
b) By how much would your answer to part (a) be reduced if a second drive-thru window, with its own server, were added?