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

1/T + 1/T + 1/T = 1/12.
3/T = 1/12,
T/3 = 12,
T = 36 hours for 1 pipe.