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    Question

    'Ravi' can complete some work alone in 25 days. 'Shyam'

    is twice as efficient as 'Mohan' and four times as efficient as 'Ravi'. If 'Ravi' and 'Mohan' start working together, then after how many days should 'Shyam' replace them so that the work gets completed in exactly 10 days?
    A 5 days Correct Answer Incorrect Answer
    B 12 days Correct Answer Incorrect Answer
    C 8 days Correct Answer Incorrect Answer
    D 10 days Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ, Let the total work be 100 units. Efficiency of 'Ravi' = 100 ÷ 25 = 4 units/day Efficiency of 'Shyam' = 4 X 4 = 16 units/day Efficiency of 'Mohan' = 16 ÷ 2 = 8 units/day Let the number of days for which 'Shyam' worked alone be 'd'. So, (d X 16) + (10 - d) X (4 + 8) = 100 Or, 16d + 120 - 12d = 100 Or, 'd' = 5 So, 'Shyam' worked alone for 5 days 'Shyam' should've joined them after (10 - 5) = 5 days

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