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    Question

    Arjun covers a distance of 96 km downstream and then

    returns the same distance upstream, completing the entire journey in 7 hours. Given that the speed of the stream is 4 km/h, what is the speed of the boat in still water?
    A 7 hrs Correct Answer Incorrect Answer
    B 5 hrs Correct Answer Incorrect Answer
    C 6 hrs Correct Answer Incorrect Answer
    D 4 hrs Correct Answer Incorrect Answer

    Solution

    ATQ;
    Let boat speed in still water = b km/h
    Downstream speed = b + 4
    Upstream speed = b – 4
    Total time = (96 ÷ (b + 4)) + (96 ÷ (b – 4)) = 7
    Checking the factors of 96, (28+4 and 28−4 are both factors)
    Check: downstream = 28 + 4 = 32 km/h, upstream = 28 – 4 = 24 km/h
    Time = 96/32 + 96/24 = 3 + 4 = 7 hours

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