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    Question

    A tank can be filled by pipe M in

    data-start="1806" data-end="1818">20 hours and by pipe N in 30 hours . Pipe O is 50% more efficient than pipe M. Pipes N and O are opened when the tank is empty and turned off after 9 hours . How long will pipe M alone take to fill the remaining part?
    A 1 hrs Correct Answer Incorrect Answer
    B 0.5 hrs Correct Answer Incorrect Answer
    C 2.5 hrs Correct Answer Incorrect Answer
    D 5.4 hrs Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ,

    Let total capacity of the tank be 60 units {LCM of (20 and 30)} Efficiency of pipe M = 60/20 = 3 units/hour Efficiency of pipe N = 60/30 = 2 units/hour Efficiency of pipe O = 1.5 × 3 = 4.5 units/hour Water filled by pipe N and O in 9 hours = (2 + 4.5) × 9 = 58.5 units Remaining = 60 – 58.5 = 1.5 units Time taken by pipe M = 1.5 / 3 = 0.5 hours

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