A tank has a leak which would empty the completely filled tank in 10 hours. lf the tank is full of water and a tap is opened which admits 4 litres of water per minute in the tank, the leak takes 15 hours to empty the tank. How many litres of water does the tank hold?

Correct Answer: 7200 l

1/10-1/15

3-2/30

Pipe A is emptying at 3 units/ hr

When filling pipe ‘B’ start functioning then emptying rate comes down to 2 units/hr

So filling pipe efficiency is(3−2)=1 unit/ hr

Pipe ‘B’ will fill tank in

=30/1=30 hrs

filling rate is 4 litres / minute

It will fill 4×60=240 litres/hr

Total capacity =240×30

= 7200 litres