A tap can fill a cistern in 10 minutes, and another tap can empty it in 12 minutes. If both the taps are open, the time (in hours) taken to fill the tank will be:
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 1 hour.
The filling rate of the first tap = 1/10 of the cistern per minute
The emptying rate of the second tap = 1/12 of the cistern per minute
= (1/10) - (1/12) = 1/60
Time required to fill the tank = 1/(1/60) = 60 minutes = 1 hour