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    Question

    A work can be completed by ‘A’ and ‘B’, alone in

    15 days and 20 days, respectively. Find the number of days taken by ‘C’ to complete the same work alone if ‘A’, ‘B’ and ‘C’ together can complete the whole work in 4 days.
    A 7.5 days Correct Answer Incorrect Answer
    B 3.5 days Correct Answer Incorrect Answer
    C 4.5 days Correct Answer Incorrect Answer
    D 6.5 days Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let total work = 60 units (LCM of 15 and 20) Efficiency of ‘A’ = (60/15) = 4 units/day Efficiency of ‘B’ = (60/20) = 3 units/day Combined efficiency of ‘A’, ‘B’ and ‘C’ = (60/4) = 15 units/day Efficiency of ‘C’ = 15 – (4 + 3) = 8 units/day Required time taken = (60/8) = 7.5 days

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