Question

    The speed of a boat while moving downstream is 80% higher

    than its speed while moving upstream. If the boat covers a distance of 720 km downstream in 20 hours, determine the speed of the boat in still water.
    A 28 km/h Correct Answer Incorrect Answer
    B 20 km/h Correct Answer Incorrect Answer
    C 33 km/h Correct Answer Incorrect Answer
    D 18 km/h Correct Answer Incorrect Answer

    Solution

    ATQ;
    Let speed of the boat in still water and speed of 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 = (720/20) = 36 km/h
    ATQ,
    (x + y) = 36 ------- (I)
    And, 36 = 1.8 × (x – y)
    Or, (x – y) = 20 -------- (II)
    By adding equation (I) and equation (II), we get
    x = 28
    Therefore, speed of boat in still water = 28 km/h

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