Question

    A boatman rows 5 km in 10 minutes, along the stream and

    20 km in 2 hours against the stream. The speed of the stream is:
    A 20 km/hr Correct Answer Incorrect Answer
    B 5 km/hr Correct Answer Incorrect Answer
    C 18 km/hr Correct Answer Incorrect Answer
    D 10 km/hr Correct Answer Incorrect Answer
    E 12 km/hr Correct Answer Incorrect Answer

    Solution

    Rate downstream = 5/10 x 60 = 30 km/hr Rate upstream = 20/2 = 10 km/hr Speed of current = 1/2 (Rate downstream – Rate upstream) ⇒ 1/2 (30 – 10) km/hr = 10 km/hr

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