Question

    A man can row at a speed of 64 km/h in still water to a

    certain upstream point and back to the starting point in a river which flows at 8 km/h. Find his average speed for total journey.                                                                      
    A 60 km/hr Correct Answer Incorrect Answer
    B 65 km/hr Correct Answer Incorrect Answer
    C 70 km/hr Correct Answer Incorrect Answer
    D 63 km/hr Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Speed upstream = 64 – 8 = 56 km/hr. Speed downstream = 64 + 8 = 72 km/hr. Average speed = x/y = (2xy)/(x + y) =  (2 x 56 x 72)/(56 + 72) = 63 km/hr

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