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    Question

    When travelling with the current, a man takes 9 hours to

    cover the distance that he would've covered in 15 hours while travelling against the current. If the current flows at 6 km/h, then find the time taken by the boat to cover 36 km in still water.
    A 60 minutes Correct Answer Incorrect Answer
    B 120 minutes Correct Answer Incorrect Answer
    C 45 minutes Correct Answer Incorrect Answer
    D 90 minutes Correct Answer Incorrect Answer
    E 80 minutes Correct Answer Incorrect Answer

    Solution

    Let the speed of the boat in still water be 'x' km/hr Therefore, distance covered in upstream = 15 X (x - 6) km Also, distance covered in downstream = 9 X (x + 6) km According to the question, 15 X (x - 6) = 9 X (x + 6) Or, {(x + 6)/(x - 6)} = (15/9) = (5/3) Or, 3x + 18 = 5x - 30 Or, 2x = 48 => 'x' = 24 So, speed of the boat in still water = 24 km/h So, required time = (36/24) X 60 = 90 minutes

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