A cistern has two taps. One fills it in 12 minutes, the other empties it in 20 minutes. If both are opened, how long to fill?
✓ Correct Answer: Option A
Net rate = 1/12 − 1/20 = (5−3)/60 = 2/60 = 1/30 per minute. Time = 30 minutes.
Net rate = 1/12 − 1/20 = (5−3)/60 = 2/60 = 1/30 per minute. Time = 30 minutes.