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    Question

    Pipe ‘A’ can fill a tank in 6 hours whereas pipe

    ‘B’ can empty it in 18 hours. If both pipes are opened together while pipe ‘B’ is closed after 2 hours, then find the time taken by pipe ‘A’ to fill the rest of the tank.
    A 12 hrs Correct Answer Incorrect Answer
    B 8 hrs Correct Answer Incorrect Answer
    C 9 hrs Correct Answer Incorrect Answer
    D 5 hrs Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ; Let the capacity of the tank be 18 litres. {LCM (6 and 18)} Efficiency of inlet pipe ‘A’ = (18/6) = 3 litres/hour Efficiency of outlet pipe ‘B’ = (18/18) = 1 litre/hour Combined efficiency of both pipes = (3 – 1) = 2 litres/hour Required time = {18 – (2 × 2)} ÷ 3 = 5 hours

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