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    Question

    ‘A’ alone can complete a work in 10 days. ‘B’ alone can complete the same work in 15 days. If ‘A’ and ‘B’ work together for 3 days, then the remaining work can be completed by ‘A’ alone in how many days?

    A 3 days Correct Answer Incorrect Answer
    B 4 days Correct Answer Incorrect Answer
    C 5 days Correct Answer Incorrect Answer
    D 7 days Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let the total amount of work = 30 units {LCM of 10 and 15} Then, efficiency of ‘A’ = 30/10 = 3 units/day Efficiency of ‘B’ = 30/15 = 2 units/day Combined efficiency of ‘A’ and ‘B’ = 3 + 2 = 6 units/day Work completed by ‘A’ and ‘B’ together in 3 days = 5 × 3 = 15 units Remaining work = 30 – 15 = 15 units Time taken by ‘A’ alone to complete the remaining work = 15/3 = 5 days

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