Question : An inlet pipe can fill an empty tank in 3.6 hours, while an outlet pipe can drain a completely filled tank in 6.3 hours. If both the pipes are opened simultaneously when the tank is empty, in how many hours will the tank get completely filled?
Option 1: 9
Option 2: 8.4
Option 3: 8.1
Option 4: 8.7
Correct Answer: 8.4
Solution :
The rate at which the inlet pipe can fill the tank is 1 tank per 3.6 hours, or
The rate at which the outlet pipe can drain the tank is 1 tank per 6.3 hours, or
When both pipes are opened simultaneously, the net rate of filling the tank is the rate of the inlet pipe minus the rate of the outlet pipe.
⇒
⇒
⇒
⇒
Hence, the correct answer is 8.4.
