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    Question

    A boat takes 20 hours to cover 'n' km in still water.

    While traveling downstream, it takes 15 hours to cover (n - 50) km. If the speed of the boat in still water is 5 times the speed of the stream, find the speed of the stream.
    A 20 km/h Correct Answer Incorrect Answer
    B 5 km/h Correct Answer Incorrect Answer
    C 12 km/h Correct Answer Incorrect Answer
    D 15 km/h Correct Answer Incorrect Answer
    E none of these Correct Answer Incorrect Answer

    Solution

    ATQ, Let the speed of the stream be 'y' km/h So, speed of the boat in still water = 5 × y = '4y' km/h ATQ; (n/5y) = 20 Or, n = '100y' ...... (I) Downstream speed of the boat = 5y + y = '6y' km/h ATQ; {(n - 50) /6y} = 15 Or, n - 50 = 90y ..... (II) From equations (I) and (II): So, 100y - 50 = 90y Or, 10y = 50 So, y = 5 So, speed of the stream = 5 km/h

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