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    Question

    A car driver covers the first half of his total distance

    at a speed of ‘4x’ km/h and the second half at a speed of ‘4x – 8’ km/h. If the average speed for the entire journey comes out to be 46(2/3) km/h, find the value of ‘x’. [x > 3]
    A 24 Correct Answer Incorrect Answer
    B 34 Correct Answer Incorrect Answer
    C 55 Correct Answer Incorrect Answer
    D 12 Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ,

    {2 × 4x × (4x – 8)}/{4x + 4x – 8} = 140/3

    Or, x(4x – 8)/(8x – 8) = 35/3

    Or, 3x(4x – 8) = 35(8x – 8)

    Or, 12x² – 24x = 280x – 280

    Or, 12x² – 304x + 280 = 0

    Or, 12x² – 288x – 16x + 280 = 0

    Or, 12x(x – 24) – 16(x – 24) = 0

    Or, (12x – 16)(x – 24) = 0

    Or, x = 24 or, x = 4/3

    So, x = 24

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