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    Question

    A boat's speed while moving downstream is 60% higher

    than its speed while moving upstream. If the boat covers 720 km downstream in 18 hours, determine its speed in still water.
    A 28.5 km/h Correct Answer Incorrect Answer
    B 20.5 km/h Correct Answer Incorrect Answer
    C 32.5 km/h Correct Answer Incorrect Answer
    D 18.5 km/h Correct Answer Incorrect Answer

    Solution

    ATQ; Let the speed of the boat in still water and the speed of the stream be ‘x’ km/h and ‘y’ km/h, respectively. Downstream speed of the boat = (x + y) km/h Upstream speed of the boat = (x – y) km/h Downstream speed of the boat = (720/18) = 40 km/h
    According to the given condition, (x + y) = 40 ------- (I) And, 40 = 1.6 × (x – y) Or, (x – y) = 40 / 1.6 = 25 -------- (II) By adding equation (I) and equation (II), we get x = 32.5 km/h Therefore, the speed of the boat in still water = 32.5 km/h

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