A harvesting crew that follows the wheat harvest has two combines, each requiring service at an average rate of once every $40$ hours according to an exponential distribution. The firm has a mechanic who needs four hours to complete the average repair with exponential service times.

FINITE$-$SOURCE MODEL

Average utilization of the system

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Probability that n customers are in the system

Probability that zero customers in the service system

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Average number of customers in the service system

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Average number of customers in the waiting line

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Average time spent in the system, including service

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Average waiting time in line

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What is the probability that there will be no combines in the repair system?