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    Question

    A alone can complete 70% of a work in 21 days while B

    takes 15 days more than A to complete it. If B and C together can complete the work in 20 days, then find the time taken by C alone to complete the same work.
    A 72 days Correct Answer Incorrect Answer
    B 32.5 days Correct Answer Incorrect Answer
    C 30 days Correct Answer Incorrect Answer
    D 36 days Correct Answer Incorrect Answer

    Solution

    Time taken by A alone to complete the entire work = 21/0.7 = 30 days Time taken by B alone to complete the entire work = 30 + 15 = 45 days Let the total work = L.C.M of 30, 45 and 20 = 180 units Then, efficiency of B = (180/45) = 4 units/day Combined efficiency of B and C = (180/20) = 9 units/day So, efficiency of C alone = 9 – 4 = 5 units/day So, time taken by C alone to complete the entire work = (180/5) = 36 days

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