SOLUTION: it takes 4 hours to fill a tank it takes 6 hours to empty the tank how long dose it take to fill it if both vales are open

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Question 359395: it takes 4 hours to fill a tank it takes 6 hours to empty the tank how long dose it take to fill it if both vales are open
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Rate*Time=Output
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.
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Let the tank volume be V.
Find the fill rate,
R%5Bf%5D%2At=V
R%5Bf%5D%2A4=V
R%5Bf%5D=V%2F4
Find the drain rate,
R%5Bd%5D%2At=V
R%5Bd%5D%2A6=V
R%5Bd%5D=V%2F6
Now find the time to fill the tank when both valves are open,
%28R%5Bf%5D-R%5Bd%5D%29%2At=V
%28V%2F4-V%2F6%29%2At=V
%281%2F4-1%2F6%29%2At=1
%283%2F12-2%2F12%29%2At=1
%281%2F12%29%2At=1
highlight%28t=12%29hours