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    Question

    Time taken by a boat to cover 180 km in downstream is

    the same as to cover 140 km in upstream. Find the time taken by the boat to cover 360 km in downstream, if the speed of the boat in still water is 40 km/h.
    A 12 hrs Correct Answer Incorrect Answer
    B 8 hrs Correct Answer Incorrect Answer
    C 10 hrs Correct Answer Incorrect Answer
    D 24 hrs Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ, Let the speed of the stream be 'x' km/h. ATQ: We know that, Downstream speed of a boat = Speed of the boat in still water + speed of the stream Upstream speed of a boat = Speed of the boat in still water - speed of the stream 9(40−x) = 7(40+x) 360−9x = 280+7x 16x = 80 x = 80/16 x = 5 Therefore, speed of the stream = 5 km/h Therefore, time taken to cover 360 km in downstream = 360/(40+5) = 360/45 = 8 hrs

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