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

Let P1, P2, P3 = flow from each of the pipes in gallons/hour. Assume the pool is 1000 gallons to fill!

then 12P1 + 12P2 + 12P3 = 1000

and 18P1 + 18P2 = 1000 or 12P1 + 12P2 = 666.66

Eliminating P1 & P2, we have 12P3 = 333.33 or P3 = 27.77 gallons/hour

So 1000/27.77 = 36 hours