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    Question

    β€˜A’ alone can complete a work in 15 days while

    β€˜A’ and β€˜B’ together can complete the same work in 10 days. How much percentage of the work, β€˜B’ alone can complete in 21 days?
    A 75% Correct Answer Incorrect Answer
    B 77% Correct Answer Incorrect Answer
    C 70% Correct Answer Incorrect Answer
    D 79% Correct Answer Incorrect Answer
    E 80% Correct Answer Incorrect Answer

    Solution

    Let the total work = L.C.M of 15 and 10 = 30 units Then, efficiency of β€˜A’ alone = 30 Γ· 15 = 2 units/day Combined efficiency of β€˜A’ and β€˜B’ = 30 Γ· 10 = 3 units/day So, efficiency of β€˜B’ = 3 – 2 = 1 units/day So, work done by β€˜B’ alone in 21 days = 1 Γ— 21 = 21 units So, percentage of work completed by β€˜B’ = (21 Γ· 30) Γ— 100 = 70%

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