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    Question

    Pipe ‘A’ and pipe ‘B’, together can fill 40% of

    a tank in 6 hours while pipe ‘C’ takes 35 hours to empty it. Pipe ‘A’ and pipe ‘B’ were opened together. After 12 hours, pipe ‘C’ is also opened. Find the total time taken to fill the empty tank this way.
    A 12.5hours Correct Answer Incorrect Answer
    B 17.25hours Correct Answer Incorrect Answer
    C 8.4hours Correct Answer Incorrect Answer
    D 14.5hours Correct Answer Incorrect Answer

    Solution

    Time taken by pipe ‘A’ and pipe ‘B’, together to fill the tank = 6/0.40 = 15 hours Let the total capacity of tank = 105units (LCM of 15 and 35) Efficiency of pipe (A + B) = 105/15 = 7 units/hour Efficiency of pipe ‘C’ = 105/35 = 3 units/hour Tank filled by pipe (A + B) in 28 hours = 12 × 7 = 84 units Time taken by all three pipes to fill the remaining tank = (105 – 84)/ (7 – 3) = 21/4 hrs. =.5.25hours Total time taken = 12 + 5.25 = 17.25 hours

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