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    Question

    A man rows a boat 90 kms in 4 hours downstream and

    returns upstream in 12 hours. The speed of the stream (in km per hour) is:
    A 11.25 km/hr Correct Answer Incorrect Answer
    B 4 km/hr Correct Answer Incorrect Answer
    C 8 km/hr Correct Answer Incorrect Answer
    D 7.5 km/hr Correct Answer Incorrect Answer
    E 3.75 km/hr Correct Answer Incorrect Answer

    Solution

    Rate downstream = 90/4 = 22.5 km/hr Rate upstream = 90/12 = 7.5 km/hr Now, speed of the stream = (rate downstream – rate upstream)/2 ⇒ (22.5 – 7.5)/2 = 7.5 km/hr

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