SOLUTION: the fill pipe for a tank can fill it in 4 hours, and the drain pipe can do it in 2. If both pipes are accidentally opened, how long will it take to drain a half filled tank? HELP!!

Question 125341This question is from textbook algebra: structure and method: book1
: the fill pipe for a tank can fill it in 4 hours, and the drain pipe can do it in 2. If both pipes are accidentally opened, how long will it take to drain a half filled tank? HELP!!! the answer is 2 hours, but don't know how to get there. HELP!!! This question is from textbook algebra: structure and method: book1

Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
the fill pipe for a tank can fill it in 4 hours, and the drain pipe can do it in 2. If both pipes are accidentally opened, how long will it take to drain a half filled tank?
-----------------
Fill Pipe DATA:
Time = 4 hrs/job ; Rate = 1/4 job/hr
-----------------------
Drain Pipe DATA:
Time = 2 hrs/job ; Rate = 1/2 job/hr
------------------------
Together DATA;
Time = x hrs/job ; Rate = 1/x job/hr
==========================
EQUATION:
Drain Rate - Fill Rate = together rate
1/2 - 1/4 = 1/x
Multiply thru by 4x to get:
2x - x = 4
x = 4 hrs to empty a full tank.
Therefore 2 hrs to empty a half tank.
==============
Cheers,
Stan H.
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