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    Question

    The difference between the downstream speed and the

    upstream speed of a boat is 6km/hr and the boat travels 72km from C to D (downstream) in 4 hours. Then find the speed of the boat in still water?
    A 18km/hr Correct Answer Incorrect Answer
    B 12km/hr Correct Answer Incorrect Answer
    C 15km/hr Correct Answer Incorrect Answer
    D 25km/hr Correct Answer Incorrect Answer
    E none of these Correct Answer Incorrect Answer

    Solution

    ATQ, we can say that We have given the difference between Downstream speed (Ds) and  Upstream Speed (Us) is 6km/hr Then, Ds - Us = 6…….eq1 Let the speed of Downstream(Ds) of boat be [Speed= distance/time] = 72/4 = 18km/hr Now, putting the Ds value in eq1 we will get the value for Us. = 18 – Us = 6 18 – 6 = Us 12km/hr = Us  Therefore, the speed of boat will be = (1/2) x (18 + 12)  = (1/2) x 30 = 15km/hr 

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