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    Question

    Pipes ‘A’ and ‘B’ can fill a tank in 6 hours and

    9 hours, respectively. If pipe ‘C’ is opened along with pipes ‘A’ and ‘B’, then the tank gets filled in 9 hours. Find the time taken by pipe ‘C’ to empty (1/3)th part of the same tank.
    A 5 hours Correct Answer Incorrect Answer
    B 3 hours Correct Answer Incorrect Answer
    C 2 hours Correct Answer Incorrect Answer
    D 6 hours Correct Answer Incorrect Answer

    Solution

    Let capacity of the tank = 18 litres (lcm of 6 and 9) Efficiency of pipe ‘A’ = (18/6) = 3 litres/hour Efficiency of pipe ‘B’ = (18/9) = 2 litres/hour Efficiency of all the three pipes together = (18/9) = 2 litres/hour Efficiency of pipe ‘C’ = 2 – (3 + 2) = (-3) litre/hour {Negative sign shows that pipe ‘C’ is an outlet pipe} Required time taken = {(1/3) × 18)}/3 = 2 hours

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