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    Question

    A boat travels 200 km downstream in 10 hours. The

    difference between its downstream speed and upstream speed is 5 km/h. What is the ratio of the boat's speed in still water to the speed of the stream?
    A 11:12 Correct Answer Incorrect Answer
    B 20:21 Correct Answer Incorrect Answer
    C 21:17 Correct Answer Incorrect Answer
    D 7:1 Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ;
    Downstream speed = 200 ÷ 10 = 20 km/h
    Let boat speed in still water = b, stream speed = s
    Downstream = b + s = 20
    Upstream = b – s
    Difference between downstream and upstream = (b + s) – (b – s) = 2s = 5
    Hence s = 2.5
    Then b = 20 – s = 17.5
    Required ratio = 17.5 : 2.5 = 7 : 1

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