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    Question

    A motorcyclist travels the first

    half of his trip at a speed of 4x km/h and the second half at a speed of 4x – 10 km/h. If his average speed for the full journey is 44 km/h, find the value of x. [x > 5]
    A 18 Correct Answer Incorrect Answer
    B 11 Correct Answer Incorrect Answer
    C 16 Correct Answer Incorrect Answer
    D 13 Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    According to the question, (2 Γ— 4x Γ— (4x – 10)) / (4x + 4x – 10) = 44 β‡’ x(4x – 10) / (8x – 10) = 22 β‡’ 22(8x – 10) = x(4x – 10) β‡’ 176x – 220 = 4xΒ² – 10x β‡’ 4xΒ² – 186x + 220 = 0 β‡’ 2x(2x – 93) – 10(2x – 11) = 0 β‡’ (2x – 10)(2x – 11) = 0 β‡’ x = 11 or x = 5 ∴ x = 11

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