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    Question

    A boat, whose speed in still water is 25% more than the speed of the current, covers 810 km downstream in _____ hours. The speed of the boat in still water is ______ km.

    The values given in which of the following options will fill the blanks in the same order in which is it given to make the statement true:

    I. 20, 24

    II. 10, 45

    III. 30, 15

    A only I and II Correct Answer Incorrect Answer
    B only II and III Correct Answer Incorrect Answer
    C only I Correct Answer Incorrect Answer
    D All are true Correct Answer Incorrect Answer
    E only III Correct Answer Incorrect Answer

    Solution

    Let, the speed of the current be x km/hr Therefore, speed of the boat in still water = 1.25x km/hr Downstream speed of the boat = x + 1.25x = 2.25x km/hr For I: 2.25x = 810/20 => x = 40.5 => x = 18 Therefore, speed of boat in still water = 1.25x = 22.5 km/hr Therefore, I is false. For II: 2.25x = 810/10 => 2.25x = 81 => x = 36 Therefore, speed of boat in still water = 1.25x = 45 km/hr Therefore, II is true. For III: 2.25x = 810/30 => 2.25x = 27 => x = 12 Therefore, speed of the boat in still water = 1.25x = 15 km/hr Therefore, III is true.

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