A Cistern has an inlet pipe and outlet pipe The inlet pipe fills the cistern completely in 1 hour 20...........

Quant (SSC) Pipes&cistern

A Cistern has an inlet pipe and outlet pipe. The inlet pipe fills the cistern completely in 1 hour 20 minutes when the outlet pipe is plugged. The outlet pipe empties the tank completely in 4 hours when the inlet pipe is plugged. If both pipes are opened simultaneously at a time when the tank was one-third filled, when will the tank fill thereafter?

3 hours

2 hours

5 hours

4 hours

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Explanation:

Inlet pipe Efficiency = 100/(8/6) = 75%
Outlet pipe Efficiency = 100/(4) = 25%
Net Efficiency = 75 – 25
= 50%(1/3)filled
2/3 filled = 100%
Required time = 100/50 = 2 hours
Hence, option 2 is the correct answer.