Pipes A and B are fitted to a tank. A can fill the tank in 1½ hours and capacity of B which is emptying pipe is half that of A. If B is fitted at one-third of the height of the tank from the base and both the pipes are opened simultaneously, then time taken to fill the empty tank is:
Filling capacity of A per hour = 2/3, .'. Emptying capacity of B per hour = (1/2)*(2/3) = 1/3
As B, the emptying pipe is fitted at 1/3 of the height of the tank from base, so the draining will start only after tank is 1/3 full.
Now time taken to fill 1/3 tank by A = (1/3)/(2/3) = 1/2 hrs.
Effective filling per hour after 1/3 tank is full = 2/3 - 1/3 = 1/3
.'. Time required to fill remaining 2/3 tank = (2/3) / (1/3) = 2 hrs
Total time = (1/2 + 2) Hrs = 2 hours 30 minutes
Correct Option 8)