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    Question

    Two pipes, A and B, can fill a tank together in 72 minutes.

    Both pipes are turned on at the same time. However, pipe B is turned off after 60 minutes, and the tank gets completely filled in a total of 1 hour and 20 minutes. How long would it take for pipe B alone to fill the tank?
    A 2 hr 20 mins Correct Answer Incorrect Answer
    B 3 hr 45 mins Correct Answer Incorrect Answer
    C 2 hr 30 mins Correct Answer Incorrect Answer
    D 3 hr Correct Answer Incorrect Answer

    Solution

    Let pipe A and B can fill ‘x’ units and ‘y’ units, of water per minute.
    Total capacity of tank = 72 × (x + y) units
    According to question;
    60 × (x + y) + 20x = 72 × (x + y)
    80x + 60y = 72x + 72y
    8x = 12y
    2x = 3y
    x = 1.5y
    Desired time = 72 × (1.5y + y)/y = 180 minutes = 3 hours

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