SOLUTION: A water tank can be filled by an inlet pipe in 9 hours. It takes 4 times as long for the outlet pipe to empty the tank. How long will it take to fill the tank if both pipes are ope

Question 890791: A water tank can be filled by an inlet pipe in 9 hours. It takes 4 times as long for the outlet pipe to empty the tank. How long will it take to fill the tank if both pipes are open?
Answer by ptaylor(2198) (Show Source): You can put this solution on YOUR website!
Let x = time it takes to fill the tank if both pipes are open
Then the tank fills at the rate of 1/x tank per hour when both pipes are open
The water tank is filled at the rate of 1/9 tank per hour
The water tank is emptied at the rate of 1/(9*4)=1/36 tank per hour
So our equation to solve is:
1/9-1/36=1/x
4/36-1/36=1/x
3/36=1/x
3x=36
x=12 hrs---time it takes to fill the tank with both pipes open
CK
In 12 hours the inlet pipe fills (1/9)*12 =4/3 tank
But in 12 hrs the drain pipe drains(1/36)*12=1/3 tank
4/3 - 1/3 =3/3=1 tank
Hope this helps---ptaylor

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