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ExamsGATEGeneral Aptitude

It takes 30 minutes to empty a half-full tank by draining it at a constant rate. It is decided to simultaneously pump water into the half-full tank while draining it. What is the rate at which water has to be pumped in so that it gets fully filled in 10 minutes?

  1. 4 times the draining rate
  2. 3 times the draining rate
  3. 2.5 times the draining rate
  4. 2 times the draining rate

Correct answer: 3 times the draining rate

Solution

A half-full tank is emptied in 30 minutes, so the draining rate is half-tank per 30 minutes = 1/60 tank per minute. To go from half-full to full in 10 minutes, the net filling rate must be half-tank per 10 minutes = 1/20 tank per minute. Therefore, pump rate = net filling rate + draining rate = 1/20 + 1/60 = 1/15 tank per minute, which is 3 times the draining rate.

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