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    Question

    Speed of a boat in still water to speed of boat in

    upstream is 10:7. If the boat can travel 390 km in downstream in 5 hours, then find the time taken by the boat to cover 18 km in still water.
    A 30 minutes Correct Answer Incorrect Answer
    B 20 minutes Correct Answer Incorrect Answer
    C 15 minutes Correct Answer Incorrect Answer
    D 18 minutes Correct Answer Incorrect Answer

    Solution

    Let speed of boat in still water and speed of boat in upstream be ‘10x’ km/h and ‘7x’ km/h, respectively. Speed of stream = 10x – 7x = 3x km/h Speed of boat in downstream = 10x + 3x = 13x km/h So, 13x = 390/5 = 78 Or, x = 6 Speed of boat in still water = 10 × 6 = 60 km/h Desired time = 18/60 = 18 minutes

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