The overhead tank at a training centre holds 7,200 litres when it is full. Two pumps are attached to it: working alone, one of them takes 40 minutes to raise the tank from empty to full and the other…

Question

The overhead tank at a training centre holds 7,200 litres when it is full. Two pumps are attached to it: working alone, one of them takes 40 minutes to raise the tank from empty to full and the other takes 60 minutes to do the same. There is besides a waste pipe at the foot of the tank, which by itself would run a full tank dry in 72 minutes. One morning the tank stood empty and both the pumps were set going together, the waste pipe being shut; twelve minutes later the waste pipe was opened by mistake and was not shut again, both the pumps continuing to run until the tank was full. Reckoned from the moment at which the pumps were started, how long did the tank take to ll?

PYQPulse · Accepted Answer

30 minutes

Answer: A. 30 minutes