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    Question

    Pipe ‘A’ and pipe ‘B’,

    together can fill 20% of a tank in 7 hours while pipe ‘C’ takes 36 hours to empty it. Pipe ‘A’ and pipe ‘B’ were opened together. After 31 hours, pipe ‘C’ is also opened. Find the total time taken to fill the empty tank this way.
    A 160 hours Correct Answer Incorrect Answer
    B 175 hours Correct Answer Incorrect Answer
    C 150 hours Correct Answer Incorrect Answer
    D 145 hours Correct Answer Incorrect Answer

    Solution

    Time taken by pipe ‘A’ and pipe ‘B’, together to fill the tank = 7/0.20 = 35 hours
    Let the total capacity of tank = 1260 units
    Efficiency of pipe (A + B) = 1260/35 = 36 units/hour
    Efficiency of pipe ‘C’ = 1260/36 = 35 units/hour
    Tank filled by pipe (A + B) in 31 hours = 31 × 36 = 1116 units
    Time taken by all three pipes to fill the remaining tank = (1260 – 1116)/(36 – 35) = 144 hrs
    Total time taken = 144 + 31 = 175 hours

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