SOLUTION: An inlet pipe on a swimming pool can be used to fill the pool in 21 hours. The drain pipe can be used to empty the pool in 28 hours. If the pool is 1/2 filled and then the inlet pi

Question 1054744: An inlet pipe on a swimming pool can be used to fill the pool in 21 hours. The drain pipe can be used to empty the pool in 28 hours. If the pool is 1/2 filled and then the inlet pipe and drain pipe are opened, how long from that time will it take to fill the pool?

Answer by Alan3354(69443) (Show Source): You can put this solution on YOUR website!
An inlet pipe on a swimming pool can be used to fill the pool in 21 hours. The drain pipe can be used to empty the pool in 28 hours. If the pool is 1/2 filled and then the inlet pipe and drain pipe are opened, how long from that time will it take to fill the pool?
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The inlet fills 1/21 pool per hour.
The drain fills -1/28 per hour.
Together --> 1/21 - 1/28 pools per hour.
= 1/84 pools per hour.
--> 84 hours to fill it from empty.
Starting at 1/2 full --> 42 hours.
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