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A tank is filled in eight hours by three pipes A, B and C. Pipe A is twice as fast as pipe B, and B is twice as fast as C. How much time will pipe B alone take to fill the tank?

Correct answer: B. 28 hours

  • A. 24 hours
  • B. 28 hours
  • C. 32 hours
  • D. 36 hours

Explanation

Let C's rate be x tank/hour. Then B's rate is 2x and A's rate is 4x, so the total rate is 7x = 1/8 tank/hour; hence B's rate is 2/56 = 1/28 tank/hour. Pipe B alone therefore takes 28 hours, and the likely mistake is choosing 24 hours by confusing B's rate with A's.

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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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