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    Question

    Working alone, B can complete the work in 30 days. C is

    twice as efficient as B and A takes 20 days more than it takes C to complete the work. Working together, in how much time would they be able to complete 9 such works?
    A 77 days Correct Answer Incorrect Answer
    B 70 days Correct Answer Incorrect Answer
    C 55 days Correct Answer Incorrect Answer
    D 63 days Correct Answer Incorrect Answer
    E 75 days Correct Answer Incorrect Answer

    Solution

    Time taken by B to complete the work = 30 days
    Time taken by C to complete the work = 30/2 = 15 days
    Time taken by A to complete the work alone = 20 + 15 = 35 days
    Work done by A, B and C together in 1 day.
    ⇒ (1/30 + 1/15 + 1/35) = (7 + 14 + 6)/210 = 27/210
    this means if would take 210/27 days for A, B and C to complete the work together
    ∴ Time taken A, B and C to complete 9 works = 9 × 210/27 days = 70 days

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