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    Question

    Pipe M can fill a tank in 24 hours and pipe N in 40 hours.

    If both the pipes are opened in an empty tank, how much time will they take to fill it?
    A 14 hours Correct Answer Incorrect Answer
    B 16 hours Correct Answer Incorrect Answer
    C 15 hours Correct Answer Incorrect Answer
    D 20 hours Correct Answer Incorrect Answer

    Solution

    Let the capacity of tank be 120 litres (LCM of 24 and 40)
    Efficiency of 'M' = (120/24) = 5 litres/hour
    Efficiency of 'N' = (120/40) = 3 litres/hour
    Required time = 120 ÷ (5 + 3) = 15 hours

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