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    Question

    Pipe ‘A’ can fill a tank in 12 hours whereas pipe

    ‘B’ can empty it in 30 hours. If both pipes are opened together while pipe ‘B’ is closed after 5 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 18 hrs Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ; Let the capacity of the tank be 60 litres. {LCM (12 and 30)} Efficiency of inlet pipe ‘A’ = (60/12) = 5 litres/hour Efficiency of outlet pipe ‘B’ = (60/30) = 2 litres/hour Combined efficiency of both pipes = (5 – 2) = 3 litres/hour Required time = {60 – (3 × 5)} ÷ 5 = 9 hours

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