SOLUTION: Pipe A can fill a tank in 4 h. Pipe B can fill the tank in 9 h less than the time it takes pipe C, a drain pipe, to empty the tank. When all 3 pipes are open, it takes 2 h to fil

Question 607135: Pipe A can fill a tank in 4 h. Pipe B can fill the tank in 9 h less than the time it takes pipe C, a drain pipe, to empty the tank. When all 3 pipes are open, it takes 2 h to fill the tank. How much time is required for pipe C to empty the tank if pipe A and B are closed.
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
Add the rates of filling and subtract the
rate of emptying
A's rate: ( 1 tank filled ) / ( 4 hrs )
B's rate: ( 1 tank filled ) / ( C's rate minus 9 hrs )
C's rate: ( 1 tank emptied ) / ( x hrs )
--------
When all 3 pipes are open, it takes 2 hrs to fill the tank.

Multiply both sides by

Use quadratic formula

( ignore the negative square root )
--------------
If A and B are closed, C can empty the tank in 12 hrs

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