=12.17.* Hugh’s Repair Shop specializes in repairing German and Japanese cars. The shop has two mechanics. One mechanic works on only German cars and the other mechanic works on only Japanese cars. In either case, the time required to repair a car has an exponential distribution with a mean of 0.2 days. The shop’s business has been steadily increasing, especially for German cars. Hugh projects that, by next year, German cars will arrive randomly to be repaired at a mean rate of four per day, so the time between arrivals will have an exponential distribution with a mean of 0.25 days. The mean arrival rate for Japanese cars is projected to be two per day, so the distribution of interarrival times will be exponential with a mean of 0.5 days.

For either kind of car, Hugh would like the average waiting time in the shop before the repair is completed to be no more than 0.5 days.