Work Breakdown Structure

A crew of mechanics at the Highway Department garage repair vehicles that break down at
an average of 10 vehicles per hour (approximately Poisson in nature). The mechanic crew can
service an average of 2 vehicles every 10 minutes with a repair time distribution that
approximates an exponential distribution. The crew cost is approximately $50 per hour. The
cost associated with lost productivity from the breakdown is estimated at $80 per vehicle per
hour (or any fraction thereof). Which is cheaper, the existing system with one service crew, or
a revised system with two service crews? The average waiting time for adding the second crew
is 0.02.

(b) Peter’s International Barbershop is a popular haircutting and styling saloon near the
campus of the Brooklyn College. One barber is available to work full time and spend an
average of 3 minutes on each customer. Customers arrive all day long at an average rate
of 4 minutes Arrivals tend to follow the Poisson distribution, and service times are
exponentially distributed. Explain your results.
(a) What is the probability that the shop is empty?
(b) What is the average number of customers in the barbershop?
(c) What is the average time spent in the shop?
(d) What percentage of time the barber is busy?
(e) What is the average number of customers waiting to be served?