If 2 pipes are both open, they can fill a pool in 1 hour and 12 minutes. One of the pipes can fill the pool by itself in 2 hours. How long would it take the other pipe to fill the pool by itself?

Given both pipes can fill the pool in 1 h 12 mins = 72 mins

Given one pipe can fill the pool in 2 h = 120 mins

Let the other pipe fill the pool in x mins

Pipe 1:

120 mins = 1 pool

1 min = 1/120 pool

Pipe 2:

x mins = 1 pool

1 min = 1/x pool

Both pipes need 72 mins to fill up the pool:

72 (1/x + 1/120) = 1

72 (x + 120) / 120x = 1

72x + 8640 = 120x

120x - 72x = 8640

48x = 8640

x = 180 mins = 3 hours

Answer: It takes 3 hours for the other pipe to fill the pool.