Question: Suppose a mechanic is assigned to two machines that must be repaired whenever they break down. In this case the customers are the two machines. Suppose for each machine the running time between breakdowns is known to be exponentially distributed with a mean running time of 3 hr. The service time required by the mechanic to get either of the machines running is also exponentially distributed with the mean service time being 30 min. Suppose we wish to know. under steady-state conditions, what fraction of the time all the machines are running.
1. What is the expected number of machines in service?