SOLUTION: One pipe can fill a tank in 5 hours and another pipe can fill the same tank in 4 hours. A drainpipe can empty the full content of the tank in 20 hours. With all the three pipes ope

Algebra ->  Rate-of-work-word-problems -> SOLUTION: One pipe can fill a tank in 5 hours and another pipe can fill the same tank in 4 hours. A drainpipe can empty the full content of the tank in 20 hours. With all the three pipes ope      Log On


   

Question 745076: One pipe can fill a tank in 5 hours and another pipe can fill the same tank in 4 hours. A drainpipe can empty the full content of the tank in 20 hours. With all the three pipes open, how long will it take to fill the tank?
Found 2 solutions by nerdybill, Alan3354:
Answer by nerdybill(7384) About Me  (Show Source):
You can put this solution on YOUR website!
One pipe can fill a tank in 5 hours and another pipe can fill the same tank in 4 hours. A drainpipe can empty the full content of the tank in 20 hours. With all the three pipes open, how long will it take to fill the tank?
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Let x = time (hours) it takes to fill tank
then
x(1/5 + 1/4 - 1/20) = 1
multiplying both sides by 20:
x(4 + 5 - 1) = 20
x(8) = 20
x = 20/8
x = 5/2
x = 2.5 hours

Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
One pipe can fill a tank in 5 hours and another pipe can fill the same tank in 4 hours. A drainpipe can empty the full content of the tank in 20 hours. With all the three pipes open, how long will it take to fill the tank?
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In each hour, the 1st pipe adds 1/5 of the tank, the 2nd adds 1/4 of the tank, and the drain adds -1/20 of the tank.
--> (1/5 + 1/4 - 1/20) tank/hour
Hours/tank = 1/(1/5 + 1/4 - 1/20)