Two taps fill a cistem at the rate of 1 litre per minute and 2 litres per minute, respectively. A third tap empties it at rate of \(\frac{1}{2}\) litre per minute. If the capacity of the cistem is 1000 litres, then how much time will it take to fill it if all the three taps are open ?
1
7 hrs
2
6 hrs 40 min
3
6 hrs 30 min
4
6 hrs