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    Question

    A boat can cover a distance of 64 km downstream in 4

    hours less time than it takes to travel the same distance upstream. If the current of the stream flows at a speed of 4 km/h, determine the speed of the boat in still water.
    A 15 km/hr Correct Answer Incorrect Answer
    B 14 km/hr Correct Answer Incorrect Answer
    C 12 km/hr Correct Answer Incorrect Answer
    D 8 km/hr Correct Answer Incorrect Answer
    E 16 km/hr Correct Answer Incorrect Answer

    Solution

    Let the speed of boat in the still water be ‘x’ km/h. ATQ, {64/(x – 4)} – {64/(x + 4)} = 4 Or,{64 × (x + 4 – x + 4)}/(x2 – 42) = 4 Or, 16 × 8 = (x2 – 42) Or, x2 = 128 + 16 Or, x2 = 144 Or, x = √144 So, x = 12 [Since, the speed of the boat cannot be negative] So, the speed of boat in still water = 12 km/hr

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