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    Question

    ‘R’ alone can build a wall in 40 days. Together,

    ‘R’ and ‘S’ can do it in 25 days. If ‘S’ worked for 8 days alone and stopped, how many more days would ‘R’ need to complete the task?
    A 20 days Correct Answer Incorrect Answer
    B 18 days Correct Answer Incorrect Answer
    C 12 days Correct Answer Incorrect Answer
    D 10 days Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ,

    Let total work = 200 {L.C.M of 40 and 25}

    Efficiency of ‘R’ = 200 ÷ 40 = 5 units/day

    Combined efficiency of ‘R’ and ‘S’ = 200 ÷ 25 = 8 units/day

    So, efficiency of ‘S’ alone = 8 – 5 = 3 units/day

    Work done by ‘S’ in 8 days = 3 × 8 = 24 units

    Remaining work = 200 – 24 = 176 units

    Time taken by ‘R’ to finish remaining work = 176 ÷ 5 = 35.2 days

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