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Open Class Interval Problem from AS S1

  1. Jun 2, 2012 #1
    1. The problem statement, all variables and given/known data
    Question

    Anna is calculating the mean and standard deviation for a set of data for a random
    variable X. The data is summarised in the table below.

    x: 10– 20– 30– 40–50
    Frequency: 8 20 12 0

    (i) For each of the following cases, write down the appropriate mid-values of the four
    intervals.

    (a) X is the weight of a letter, in grams. (This one is okay, variable is continuous)
    (b) X is the number of misprints in a magazine. (This one is okay, variable discrete)
    (c) X is the age, in complete years, of the audience at a cinema. (Problem)

    Answers:
    (a) 15, 25, 35, 45
    (b) 14.5, 24.5, 34.5, 45
    (c) 15, 25, 35, 45.5 (3 s.f.)

    2. Relevant equations

    3. The attempt at a solution
    I understand a) and b) fine. However, I can't figure out c) since I can't figure out what type of variable it is. I initially thought it would be discrete, due to the number of *complete* years. Would that not make the answer the same as that to b) though?
    Any clarification is greatly appreciated, exams coming soon :).
     
  2. jcsd
  3. Jun 2, 2012 #2
    Problem solved.
     
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