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Pipe A can fill a tank in 6 hours. Due to a leak at the bottom, it takes 9 hours for the pipe A to fill the tank. In what time can the leak alone empty the full tank?

Correct answer: C. 18 hours

  • A. 16 hours
  • B. 15 hours
  • C. 18 hours
  • D. 17 hours

Explanation

Pipe A's rate is 1/6 tank/hour, but its net rate with the leak is 1/9 tank/hour. Therefore, the leak's rate is 1/6 - 1/9 = 1/18 tank/hour, so it empties the tank alone in 18 hours. The likely wrong choice is 15 hours, which does not follow from subtracting the net and pipe rates.

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About Time and Work

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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