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    Question

    Pipe ‘A’ and pipe ‘B’, together can fill 20% of

    a tank in 5 hours while pipe ‘C’ takes 30 hours to empty it. Pipe ‘A’ and pipe ‘B’ were opened together. After 23 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 42hours Correct Answer Incorrect Answer
    C 40 hours Correct Answer Incorrect Answer
    D 35 hours Correct Answer Incorrect Answer

    Solution

    Time taken by pipe ‘A’ and pipe ‘B’, together to fill the tank = 5/0.20 = 25 hours Let the total capacity of tank = 150 units Efficiency of pipe (A + B) = 150/25 = 6 units/hour Efficiency of pipe ‘C’ = 150/30 = 5 units/hour Tank filled by pipe (A + B) in 23 hours = 23 × 6 = 138 units Time taken by all three pipes to fill the remaining tank = (150 – 138)/(6 – 5) = 12 hrs Total time taken = 23 + 12 = 35 hours

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