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    Question

    Pipe ‘X’ alone can fill a tank in 20 hours. When

    pipe ‘X’ and ‘Y’ are opened together, they can fill 60% of the same tank in 6 hours. Find the time taken by pipe ‘Y’ alone to fill 80% of the same tank.
    A 25 hrs Correct Answer Incorrect Answer
    B 48 hrs Correct Answer Incorrect Answer
    C 22 hrs Correct Answer Incorrect Answer
    D 16 hrs Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ; Time taken by pipes ‘X’ and ‘Y’ together to fill 100% of the tank = 6 ÷ 0.6 = 10 hours Let the capacity of the tank be 100 litres. {LCM (20 and 10)} Efficiency of pipe ‘X’ = (100/20) = 5 litres/hour Efficiency of pipe ‘X’ and ‘Y’ together = (100/10) = 10 litres/hour Efficiency of pipe ‘Y’ = 10 – 5 = 5 litres/hour Time taken by pipe ‘Y’ to fill 80% of the tank = (100 × 0.8)/5 = 16 hours

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