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Question 133570: One pump can fill a water tank in 3h (hours), and another pump takes 5h. When the tank was empty, both pumps were turned on for 30 minutes and then the faster pump was turned off. How much longer did the slower pump have to run before the tank was filled?
Answer by ptaylor(2198)   (Show Source):
You can put this solution on YOUR website! One pump can fill a water tank in 3h (hours), and another pump takes 5h. When the tank was empty, both pumps were turned on for 30 minutes and then the faster pump was turned off. How much longer did the slower pump have to run before the tank was filled?
Let x= amount of time slow pump had to run after faster pump was cut off
The faster pump fills at the rate of 1/3 tank per hour
The slower pump fills at the rate of 1/5 tank per hour
Together they fill at the rate of 1/3 + 1/5 or 5/15+3/15 tank per hour
and this equals:
8/15 tank per hour
So, working together they can fill (8/15)*(1/2) or 8/30 of the tank in 30 min and that leaves (30/30)-(8/30) or 22/30 or 11/15 of the tank yet to be filled.
So our equation to solve is:
(1/5)x=11/15 multiply each side by 15
3x=11 divide both sides by 3
x= 3 2/3 hours------------------------amount of time slow pump had to run after faster pump was cut off
Hope this helps---ptaylor
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