• • • D.19 One mechanic services 5 drilling machines for a steel plate manufacturer. Machines break down on an average of once every 6 working days, and breakdowns tend to follow a Poisson distribution. The mechanic can handle an average of one repair job per day. Repairs follow a negative exponential distribution.

a) On the average, how many machines are waiting for service?

b) On the average, what is the waiting time to be serviced?