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A tank is filled in 5 hours by three pipes A, B and C. The pipe C is twice as fast as B and B is twice as fast as A. How much time will pipe A alone take to fill the tank?

Correct answer: C. 35 hrs

  • A. 20 hrs
  • B. 25 hrs
  • C. 35 hrs
  • D. Cannot be determined

Explanation

Let pipe A's rate be x tank/hour. Then B works at 2x tank/hour and C at 4x tank/hour, so 7x = 1/5 tank/hour, giving x = 1/35 tank/hour and a time of 35 hours. The likely mistake is choosing 25 hours by adding the speed ratios incorrectly instead of using the total ratio 1:2:4.

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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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