Multiple choice

The mixing tank of an effluent treatment plant (ETP) is in the form a right circular cylinder with a uniform cross section. It has an adjustable outlet pipe that can be attached to the tank at any height desired. The outlet pipe drains water out of the tank via a pump at a constant rate irrespective of the height it is attached at. The tank is filled at a constant rate using another inlet pipe. If the outlet pipe is attached at half the height of the tank, the tank which is initially empty gets filled in 18 hours. If the outlet pipe is attached at height equal to 2/3rd the height of the tank, the tank which is initially empty gets filed in 16 hours. In how many hours will the tank, that is initially empty, be completely filled, if the outlet pipe is not attached to the tank?

  1. 8

  2. 9

  3. 12

  4. 14
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let the filling-only time be p and the effective filling time above the outlet be q. The two cases give p + q = 36 and 2p + q = 48, so p = 12 hours. With no outlet attached, the tank fills in 12 hours.

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