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    Marks in statistics of 12 students are x, 28, 35, 56, 78, 63, 65, 81, 79, 83, 80, y, where x and y are the lowest and highest marks, respectively
    Question

    Marks in statistics of 12 students are x, 28, 35, 56, 78, 63, 65, 81, 79, 83, 80, y, where x and y are the lowest and highest marks, respectively. If the range and average of the marks are 70 and 64, respectively, then the ordered pair (x, y) is:​

    A.

    (23, 93)

    B.

    (35, 105)

    C.

    (25, 95)

    D.

    (30, 100)

    Correct option is C

    Given:

    Marks: (x, 28, 35, 56, 78, 63, 65, 81, 79, 83, 80, y)

    x = lowest, y = highest

    Range = 70

    y - x = 70

    Average = 64

    Formula Used:

    Sum =Average×Number of observations \text{Average} \times \text{Number of observations}​​

    Range = Max - Min

    Solution:
    total of 12 marks = 64×12=7684 \times 12 = 768​​

    Sum of known 10 marks
    28 + 35 + 56 + 78 + 63 + 65 + 81 + 79 + 83 + 80 = 648.
    So,
    x + y + 648 = 768 

    x + y = 120
    Also,
    y - x = 70
    Solve the system:
    Now,

    2y = 190

    y = 95

    x = 120 - 95 = 25.
    (x, y) = (25, 95)

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