Question

When three pipes fill a pool, they can finish in 12 hours. Two of the pipes can finish in 18 hours if they are working together. How long would it take a third pipe to fill the pool on its own?

Answer 1

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18 hours

Answer 2

3 pipes take 12 hours
⇒ In 1 hour, the 3 pipes can fill 1/12 of the pool

2 of the pipes take 18 hours
⇒ in 1 hour, the 2 pipes can fill 1/18 of the pool

In 1 hour, the third pipe alone can fill :


`(1)/(12) - (1)/(18) = (3)/(36) - (2)/(36) = (1)/(36) \text { of the pool}`

Time needed :


`1 / (1)/(36) = 1 * 36 = 36 \text { hours}`

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Answer: It will take 36 hours for the third pipe to fill the pool.
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