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Puzzle No. 3

Posted on 15 January 2016

There is a 100-liter water tank; whose input pump can be used to fill it at the rate of 1 liter every 2 minutes; and the outlet valve can consume 1 liter every 5 minutes.
The tank contained 80 liters when the outlet valve was opened at 10:00 AM. If the tank now contains 50 liters of water at 3:00 PM, then for how many minutes has the input pump remained active?

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