One pipe can fill a tank four times as fast as another pipe. If together the two pipes can fill the tank in 48 minutes, the slower pipe alone will be able to fill the tank in:
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 240 minutes.
Let the time taken by the slower pipe to fill the tank be x minutes.
The faster pipe is four times as fast, it will take x/4 minutes to fill the tank.
In one minute, the slower pipe fills 1/x of the tank
In one minute, the faster pipe fills 1/(x/4) = 4/x of the tank
Working together, two pipes fill = (1/x) + (4/x) = 5/x of the tank per minute
So, 5/x = 1/48
⇒ x = 240
Therefore, the slower pipe alone will be able to fill the tank in 240 minutes.