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    Question

    ‘A’ alone can complete a work in 50 hours. ‘A’ started the work alone and left after working on it for 20 hours. If ‘B’ completed the rest of the work in 10 hours then find the time taken by ‘A’ and ‘B’ together to complete the whole work.

    A 10.5 hours Correct Answer Incorrect Answer
    B 9.5 hours Correct Answer Incorrect Answer
    C 12.5 hours Correct Answer Incorrect Answer
    D 11.5 hours Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let the total work = 200 units Then, efficiency of ‘A’ = (200/50) = 4 units/hour Work completed by ‘A’ alone in 20 hours = 4 × 20 = 80 units Remaining work = 200 – 80 = 120 units So, efficiency of ‘B’ = 120/10 = 12 units/hour Therefore, combined efficiency of ‘A’ and ‘B’ = 12 + 4 = 16 units/hour So, time taken by ‘A’ and ‘B’ together to complete the work = (200/16) = 12.5 hours

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