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    Question

    A fence is constructed using 900 wooden planks. ‘X’

    alone can place 10 planks per minute, while ‘Y’ alone can complete the fence in 100 minutes. ‘Z’, a curious kid, removes 4 planks per minute. If all three work together, how long will it take to finish the fence?
    A 1 hrs Correct Answer Incorrect Answer
    B 2 hrs Correct Answer Incorrect Answer
    C 5 hrs Correct Answer Incorrect Answer
    D 8 hrs Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ,

    Efficiency of ‘Y’ = (900 / 100) = 9 planks/minute So, combined efficiency of ‘X’, ‘Y’ and ‘Z’ = 10 + 9 – 4 = 15 planks per minute So, time taken to build the fence = (900 / 15) = 60 minutes = 1 hour

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