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Question 551199: A water tank has two valves, A and B. When only valve A is open, the tank is emptied in 10 minutes Furthermore, it takes twenty minutes to empty the tank if only valve B is open. How long will it takes to empty the tank if both valves are open?
Answer by lwsshak3(11628)   (Show Source):
You can put this solution on YOUR website! A water tank has two valves, A and B. When only valve A is open, the tank is emptied in 10 minutes Furthermore, it takes twenty minutes to empty the tank if only valve B is open. How long will it takes to empty the tank if both valves are open
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Valve A can empty the tank in 10 minutes by itself
so its work rate=1/10
Valve B can empty the tank in 20 minutes by itself
so its work rate=1/10
With both valves open, they can empty the tank in x minutes
so the work rate for both valves open=1/x
sum of individual work rates=work rate when working together
..
1/10+1/15=1/x
x/10+x/15=1
3x/30+2x/30=1
5x/30=1
5x=30
x=6
ans:
It will take 6 minutes to empty the tank if both valves are open
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