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A tap can fill a tank in 32 min. and another can empty it in 16 min. If the tank is already half full and both the tanks are opened together, the tank will be_________?

Correct answer: C. 16 min

  • A. 12 min
  • B. 14 min
  • C. 16 min
  • D. 20 min

Explanation

The filling rate is 1/32 tank per minute and the emptying rate is 1/16 tank per minute, so the net rate is 1/32 - 2/32 = -1/32 tank per minute. Starting with half a tank, the time to empty it is (1/2) / (1/32) = 16 minutes. The likely mistake is 12 minutes, which does not account correctly for the half-tank starting amount and the net rate.

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Problems measure work through rates, treating each person's or machine's contribution as work completed per unit time. Questions cover combined work, efficiency, wages, alternate working schedules, pipes and cisterns, and men-days relationships, with care needed to distinguish time taken by one worker from the time required when workers act together.

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