SOLUTION: One pipe fills a storage pool in 12 hours. A second pipe fills the same pool in 3 hours. When a third pipe is added and all three are used to fill the pool, it takes only 2 hours

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Question 589726: One pipe fills a storage pool in 12 hours. A second pipe fills the same pool in 3 hours. When a third pipe is added and all three are used to fill the pool, it takes only 2 hours. Find how long it takes the third pipe to do the job.
I have trouble setting it up, but I know how to do it, please help!
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
One pipe fills a storage pool in 12 hours.
A second pipe fills the same pool in 3 hours.
When a third pipe is added and all three are used to fill the pool, it takes only 2 hours.
Find how long it takes the third pipe to do the job.
:
Let x = time required by the 3rd pipe
Let the completed job = 1; (a full tank)
:
2%2F12 + 2%2F3 + 2%2Fx = 1
Multiplying by 12x will clear the denominators