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Two pipes A and B can fill a tank in 20 and 30 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?

Correct answer: A. 12 min

  • A. 12 min
  • B. 15 min
  • C. 25 min
  • D. 50 min

Explanation

The two pipes supply 1/20 + 1/30 = 3/60 + 2/60 = 1/12 tank per minute. Thus, working together, they fill the tank in 12 minutes. The likely wrong choice is 15 minutes, which results from averaging the two stated times instead of adding their 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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