A and B can complete a work in 15 days and 10 days respectively. They started doing the work together but after 2 days B had to leave and A alone completed the remaining work. The whole work was completed in___________?
Correct answer: C. 12 days
- A. 8 days
- B. 10 days
- C. 12 days
- D. 15 days
Explanation
Together A and B complete 1/15 + 1/10 = 1/6 work per day, so in 2 days they complete 1/3 of the work. The remaining 2/3 takes (2/3) ÷ (1/15) = 10 days for A alone, making the total 2 + 10 = 12 days. The likely trap is 10 days, which omits the first 2 days of joint work.
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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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