A fast-food franchise is considering operating a drive-up window food-service operation. Assume that customer arrivals follow a Poisson probability distribution, with an arrival rate of 24 cars per hour, and that service times follow an exponential probability distribu- tion. Arriving customers place orders at an intercom station at the back of the parking lot and then drive to the service window to pay for and receive their orders. The following three service alternatives are being considered:
• A single-channel operation in which one employee fills the order and takes the money from the customer. The average service time for this alternative is 2 minutes.
• A single-channel operation in which one employee fills the order while a second em- ployee takes the money from the customer. The average service time for this alterna- tive is 1.25 minutes.
• A two-channel operation with two service windows and two employees. The em- ployee stationed at each window fills the order and takes the money from customers arriving at the window. The average service time for this alternative is 2 minutes for each channel.
Answer the following questions and recommend an alternative design for the fast-food franchise:
a. What is the probability that no cars are in the system?
b. What is the average number of cars waiting for service?
c. What is the average number of cars in the system?
d. What is the average time a car waits for service?
e. What is the average time in the system?
f. What is the probability that an arriving car will have to wait for service?