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    Question

    A boat can cover 66 km upstream and 165 km downstream in

    13 hours. Speed of the stream is how much less than the speed of the boat in still water if the boat can cover 55 km upstream and 110 km downstream in 9 hours?
    A 11 km/h Correct Answer Incorrect Answer
    B 16 km/h Correct Answer Incorrect Answer
    C 18 km/h Correct Answer Incorrect Answer
    D 15 km/h Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ, Let the upstream speed and downstream speed of the boat be x km/h and y km/h, respectively. So according to question: 66/x + 165/y = 13 тАжтАжтАжтАжтАжтАж. (i) Also, 55/x + 110/y = 9 тАжтАжтАж.. (ii) Solving (i) and (ii), we get x = 11 and y = 22 So, the upstream speed and downstream speed of the boat are 11 km/h and 22 km/h, respectively. Speed of the boat in still water = (11 + 22)/2 = 16.5 km/h Speed of the stream = (22 тАУ 11)/2 = 5.5 km/h So, the desired difference = 16.5 тАУ 5.5 = 11 km/h

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