A cistern has a leak which would empty the cistern in 20 minutes. A tap is turned on which admits 4 liters a minute into the cistern, and it is emptied in 24 minutes. How many liters does the cistern hold?

A. 480 liters
B. 600 liters
C. 720 liters
D. 800 liters

Explanation:

1/x – 1/20 = -1/24

x = 120

120 * 4 = 480