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Assume that a set of test scores is normally distrbuted with a mean of 100 and a standard deviation of 20. Use the 68-95-99.7 rule to find the following quantities:
Suggest you make a drawing and label first....

a. Percentage of scores less than 100.

b. Relative frequency of scores less than 120.

c. Percentage of scores less than 140.

d. Percentage of scores less than 80.

e. Relative frequency of scores less than 60.

f. Percentage of scores greater than 120.

  • statistics -

    Z = (x - mean)/SD

    mean ± 1 SD = 68%
    mean ± 2 SD = 95%
    mean ± 3 SD = 99%

    a. In a normal distribution, mean= median. What does that tell you?

    b. 120 = mean + 1 SD

    Use this information to find your own answers. We do not do your work for you. Although it might require more time and effort, you will learn more if you do your own work. Isn't that why you go to school?

  • statistics -

    Yes, But that is why I ask for your help---I do not understand it.

  • statistics -

    Students were given an exam with 300 multiple-choice questions. The distribution of the scores was normal and mean was 195 with a standard deviation of 30. What were the scores of the students who were within one standard deviation of the mean?

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