Three pipes P, Q and R are attached to a water tank. The radii of the pipes P, Q and R are in the ratio 1 : 2 : 3, respectively. Pipe P alone can fill an empty tank in 36 hours. In how much time will the tank get filled if all the pipes are opened and tank is already half filled?
1
1.2 hours
2
1.36 hours
3
1.29 hours
4
1.5 hours