Question 887379
A pipe can fill a pool in 9 hours.  If a second pipe is also used, the pool can be filled in 3 hours.  How long would it take the second pipe alone to fill the pool.
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The 1st pipe fills 1/9 of the pool per hour.
The 2nd pipe fills 1/P of the pool per hour.
Together, they fill 1/3 of the pool per hour.
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1/9 + 1/P = 1/3