SOLUTION: 3 identical pumps,empty a large storage tank in 15hrs.How long will it take 21 such pumps to empty the same storage tank?

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Question 574758: 3 identical pumps,empty a large storage tank in 15hrs.How long will it take 21 such pumps to empty the same storage tank?
Answer by ad_alta(240) About Me  (Show Source):
You can put this solution on YOUR website!
Since the 3 pumps already emptied the tank, it wouldn't take any time at all! If we refilled it, we would expect that with 7 times the number of pumps the work would be done in 1/7 the time, or about 2 hours, 8 minutes, and 34 seconds.