SOLUTION: A pool can be filled by a pipe in 3 hours. It takes 3 times as long for another pipe to empty the pool. How long will it take to fill the pool if both popes are open? How do y

Algebra ->  Rate-of-work-word-problems -> SOLUTION: A pool can be filled by a pipe in 3 hours. It takes 3 times as long for another pipe to empty the pool. How long will it take to fill the pool if both popes are open? How do y      Log On


   

Question 364029: A pool can be filled by a pipe in 3 hours. It takes 3 times as long for another pipe to empty the pool. How long will it take to fill the pool if both popes are open?
How do you figure out this problem... I eventually found the answer but need to learn how to do it the right way.
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 volume of the pool be P.
Find the fill rate,
R%5Bf%5D%2At=P
R%5Bf%5D%2A3=P
R%5Bf%5D=P%2F3
Find the drain rate,
R%5Bd%5D%2At=P
R%5Bd%5D%2A9=P
R%5Bd%5D=P%2F9
Now, with both fill and drain valve open, find the time to fill the pool.
%28R%5Bf%5D-R%5Bd%5D%29%2At=P
Substitute,
%28P%2F3-P%2F9%29%2At=P
%283%2F9-1%2F9%29%2At=1
%282%2F9%29t=1
highlight%28t=9%2F2%29 hrs.