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    Question

    A boat goes downstream at 28 km/hr and upstream at 20

    km/hr. If it takes 14 hours to travel (x + y) km upstream when the stream speed is doubled, then what is the average of x and y?
    A 112 km Correct Answer Incorrect Answer
    B 60 km Correct Answer Incorrect Answer
    C 73 km Correct Answer Incorrect Answer
    D 85 km Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ,

    Let, speed of boat in still water and stream speed be B km/hour and s km/hour, respectively.

    So, (B + s) = 28 … (i)

    Also, (B – s) = 20 … (ii)

    Solving equation (i), and (ii), we get,

    B = 24 km/hour

    s = 4 km/hour

    According to question,

    (x + y)/(B – 2s) = 14

    (x + y) = 14 × (24 – 2 × 4) = 14 × 16 = 224 km

    Therefore, average value of x and y = (x + y)/2 = 224/2 = 112 km

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