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One pump can fill a gasoline storage in 8 hours. With a second pump working simultaneously, the tank can be filled in 3 hours.
How long would it take the second pump to fill the the tank alone?
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The rate of the first pump is of the tank volume per hour.
The rate of the two pipes, when they work simultaneously, is of the tank volume per hour.
Hence, the rate of the second pipe, when it works alone, is
- = - = =
of the tank volume per hour.
It means that it takes of an hour for the second pipe to fill the tank if it works alone.
hours = 4 hours and 48 minutes.