10 identical pipes are attached to a tank out of which some are inlets and the rest are outlets. If 5 inlet and 2 outlet pipes are opened together then the tank gets filled in 1 hour and if all pipes are opened together then 25% 'pre-filled' tank gets filled in 33.75 minutes. Find the number of outlet pipes attached to the tank?
1
3
2
4
3
5
4
6
5
7