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    Question

    A boy can swim a certain distance downstream in 5 hours

    and return in 7 hours. If the rate of stream is 4 kmph then what is the speed of boy in still water?
    A 14 kmph Correct Answer Incorrect Answer
    B 24 kmph Correct Answer Incorrect Answer
    C 20 kmph Correct Answer Incorrect Answer
    D 18 kmph Correct Answer Incorrect Answer
    E 16 kmph Correct Answer Incorrect Answer

    Solution

    Let the speed of the boy in still water be x kmph. Then, (x + 4) × 5 = (x – 4) × 7 => 5x + 20 = 7x - 28 => 2x = 48 => x = 24 kmph

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