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One pipe can fill a tank three times as fast as another pipe. If together the two pipes can fill tank in 36 min, then the slower pipe alone will be able to fill the tank in?

Correct answer: C. 144 min

  • A. 81 min
  • B. 108 min
  • C. 144 min
  • D. 192 min

Explanation

Let the slower pipe fill x tank/minute; the faster pipe fills 3x tank/minute. Together their rate is 4x = 1/36 tank/minute, so x = 1/144 tank/minute and the slower pipe alone takes 144 minutes. The common trap is 108 minutes, which comes from treating the faster pipe's rate as only twice the slower rate.

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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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