A cistern has a leak which would empty the cistern in 20 minutes. A tap is turned on which admits 6 liters a minute into the cistern, and it is emptied in 24 minutes. How many liters does the cistern hold?	Select.
A) 480  B) 287  C) 720  D) 270  E) 927
1/x - 1/20 = -1/24   x = 120   120 * 6= 
<gadget id="calculator">120 * 6</gadget>
<output>720</output>
720   Answer: 720
<result>C</result>
A cistern has a leak which would empty the cistern in 20 minutes. A tap is turned on which admits 6 liters a minute into the cistern, and it is emptied in 24 minutes. How many liters does the cistern hold?