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    Question

    Nikita covered a total distance of 400 km — partly by

    airplane at 200 km/h and partly by bus at 80 km/h. If she took 3.5 hours to reach, how many kilometers did she travel by airplane?
    A 100 km Correct Answer Incorrect Answer
    B 500 km Correct Answer Incorrect Answer
    C 600 km Correct Answer Incorrect Answer
    D 200 km Correct Answer Incorrect Answer

    Solution

    ATQ,

    Let airplane distance = d km

    Then, by bus = 400 - d km

    Time equation: d / 200 + (400 - d) / 80 = 3.5

    LCM of 200 and 80 = 400

    Or, (2d + 5(400 - d)) / 400 = 3.5

    (2d + 2000 - 5d) / 400 = 3.5

    (2000 - 3d) / 400 = 3.5

    Multiply both sides:

    2000 - 3d = 1400

    3d = 600

    d = 200

    Distance by airplane = 200 km

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