A cistern has a leak which would empty it in 8 hours. A tap is turned on which adds 6 liters a minute into the cistern and it is now emptied in 12 hours. How many liters does the cistern hold?

8640

Let capacity of the cistern be 24 units 

                       leak  :  (tap + leak)

Time taken:       8    :       12

Efficiency =       (-) 3   :  (-)2 

Efficiency of the tap = +1 = 6 lt.min (given) or = (60 x 6) lt/hr

Capacity of the cistern = 24 x 60 x 6 = 8640