Of a large stockpile of used pumps, 20% are unusable and need repair. A repairman is sent to the stockpile with three repair kits. He selects pumps at random and tests them one at a time. If a pump works, he goes on the next one. If a pump doesn’t work, he uses one of his repair kits to fix it. Suppose it takes 10 minutes to test a pump and 20 minutes to repair a pump that doesn’t work. Find the mean and standard deviation of the total time it takes the repairman to use up his three kits.

A First Course in Probability (10th Edition)
10th Edition
ISBN:9780134753119
Author:Sheldon Ross
Publisher:Sheldon Ross
Chapter1: Combinatorial Analysis
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Problem 1.1P: a. How many different 7-place license plates are possible if the first 2 places are for letters and...
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Of a large stockpile of used pumps, 20% are unusable and need repair. A
repairman is sent to the stockpile with three repair kits. He selects pumps at random and tests them one at a time. If a pump works, he goes on the next one. If a pump doesn’t work, he uses one of his repair kits to fix it. Suppose it takes 10 minutes to test a pump and 20 minutes to repair a pump that doesn’t work. Find the mean and standard deviation of the total time it takes the repairman to use up his three kits.

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