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Question:

Water flows into a container at a rate of 140 gallons per minute. The container has a small opening at the bottom that drains water at a rate of 1 gallon per second. How long will it take to fill the container to 240 gallons?

A 3 min
Explaination

The opening drains water at 1 gallon/second which is equivalent to 60 gallons/min. Therefore the net gain of water is 140 gallons/min - 60/gallons/min=80 gallons/min. To fill 240 gallons at a rate of 80 gallons/min will take 3 minutes.