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    Question

    The boat's downstream and upstream speeds are 24 km/hr and

    16 km/hr respectively. If the time taken to cover a distance of (x + y) km upstream with stream speed increased to double its normal value is 12 hours, what is the average of x and y?
    A 72 km Correct Answer Incorrect Answer
    B 60 km Correct Answer Incorrect Answer
    C 93 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) = 24 тАж (i)

    Also, (B тАУ s) = 16 тАж (ii)

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

    B = 20 km/hour

    s = 4 km/hour

    According to question,

    (x + y)/(B тАУ 2s) = 12

    (x + y) = 12 ├Ч (20 тАУ 2 ├Ч 4) = 12 ├Ч 12 = 144 km

    Therefore, average value of x and y = (x + y)/2 = 144/2 = 72 km

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