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    Question

    Pipe ‘A’ and pipe ‘B’,

    together can fill 20% of a tank in 6 hours while pipe ‘C’ takes 35 hours to empty it. Pipe ‘A’ and pipe ‘B’ were opened together. After 28 hours, pipe ‘C’ is also opened. Find the total time taken to fill the empty tank this way.
    A 30 hours Correct Answer Incorrect Answer
    B 42 hours Correct Answer Incorrect Answer
    C 40 hours Correct Answer Incorrect Answer
    D 49 hours Correct Answer Incorrect Answer
    E 35 hours Correct Answer Incorrect Answer

    Solution

    Time taken by pipe ‘A’ and pipe ‘B’, together to fill the tank = 6/0.20 = 30 hours
    Let the total capacity of tank = 210 units
    Efficiency of pipe (A + B) = 210/30 = 7 units/hour
    Efficiency of pipe ‘C’ = 210/35 = 6 units/hour
    Tank filled by pipe (A + B) in 28 hours = 28 × 7 = 196 units
    Time taken by all three pipes to fill the remaining tank = (210 – 196)/(7 – 6) = 14 hrs
    Total time taken = 28 + 14 = 42 hours

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