One pipe can fill a tank three times as fast as another pipe. If together the two pipes can fill the tank in 36 minutes, then the slower pipe alone will be able to fill the tank in?
81 min
108 min
144 min
192 min
162 min
144 min
Let the slower pipe alone fill the tank in x minutes.
∴ 1x+3x=136
4x=136 ⇔ x=144min.