Tank Inlet and Outlet Pipes

CAT 2017 Slot 2 · QA · Medium · Pipes and Cisterns

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A tank has an inlet pipe and an outlet pipe. If the outlet pipe is closed then the inlet pipe fills the empty tank in 8 hours. If the outlet pipe is open then the inlet pipe fills the empty tank in 10 hours. If only the outlet pipe is open then in how many hours the full tank becomes half-full?

  1. A.

    20

  2. B.

    30

  3. C.

    40

  4. D.

    45

Answer

A

Explanation

Let capacity of the tank be 40 units (LCM of 8 and 10).

Inlet rate (II) = 40/8=540 / 8 = 5 units/hr.

Net filling rate with outlet open (I−OI - O) = 40/10=440 / 10 = 4 units/hr.

Outlet rate (OO) = 5−4=15 - 4 = 1 unit/hr.

To make a full tank (40 units) half-full, 20 units need to be emptied.

Time required = 20/1=2020 / 1 = 20 hours.

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