<PRE><B>Question 329310</B>
A water tank has an inlet pipe and a drain pipe. 
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A full tank can be emptied in 30 minutes if the drain
is opened and an empty tank can be filled in 45 minutes
with the inlet pipe opened. 
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Emptying Pipe DATA:
time = 1/2 hr/job ; rate = 2 jobs/hr
-----------------------------------
Fill tank DATA:
time = 3/4 hr/job ; rate = 4/3 job/hr
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If both pipes are accidentally
opened when the tank is full, then how long 
will it take to empty the tank?

Together DATA:
time = x hrs/job ; rate = 1/x job/hr.
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Equation:
Empty rate - Fill rate = together rate
2 - (4/3) = 1/x
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Multiply thru by 3x to get:
6x-4x = 3
2x = 3
x = 3/2 hrs
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Cheers,
Stan H.
</PRE>