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    Question

    Ratio of speed of boat in downstream and speed of stream

    is 9:4, if speed of current is 8 km/hr, then find distance travelled (in km) upstream in 5 hours. Section 4
    A 10 km Correct Answer Incorrect Answer
    B 24 km Correct Answer Incorrect Answer
    C 40 km Correct Answer Incorrect Answer
    D 70 km Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Given: Ratio of (speed of boat in downstream) : (speed of stream) = 9 : 4 Speed of stream = 8 km/h Let common multiplier = k So, Speed of stream = 4k = 8 => k = 8 / 4 = 2 Speed of boat in downstream = 9k = 9 × 2 = 18 km/h Let speed of boat in still water = b km/h Speed of stream = 8 km/h Downstream speed = b + 8 = 18 => b = 18 - 8 = 10 km/h Upstream speed = b - speed of stream = 10 - 8 = 2 km/h Distance travelled upstream in 5 hours: = speed × time = 2 × 5 = 10 km

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