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    Question

    A boat travels 40 km downstream in 5 hours, and the same

    boat travels 40 km upstream in 8 hours. Find the speed of the boat in still water. 
    A 6.5 km/h Correct Answer Incorrect Answer
    B 8 km/h Correct Answer Incorrect Answer
    C 10 km/h Correct Answer Incorrect Answer
    D 7.5 km/h Correct Answer Incorrect Answer

    Solution

    Let the speed of the boat in still water be x km/h, and the speed of the stream be y km/h. Downstream speed = (x + y) km/h, and upstream speed = (x - y) km/h. Downstream: 40 / (x + y) = 5 Upstream: 40 / (x - y) = 8 From the downstream equation: x + y = 40 / 5 = 8. From the upstream equation: x - y = 40 / 8 = 5. Now solve: x + y = 8 x - y = 5 Adding both equations: 2x = 13 x = 6.5 km/h Thus, the speed of the boat in still water is 6.5 km/h.

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