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Assume that a set of test scores is normally distributed with a mean of 100 and a standard devaiton of 20. Use the 68-95-99.7 rule to find the following quantities:

a. percentages of scores less than 100
b. relative frequency of scores less than 120
c.percentage of scores less than 140

  • statistics -

    Here are a few hints:

    a. The mean divides a distribution in half: 50% of the distribution is above the mean and 50% of the distribution is below the mean.

    b. A score of 120 is one standard deviation above the mean.

    c. A score of 140 is two standard deviations above the mean.

    I'll let you take it from here.

  • statistics -

    a. 50%
    b. 0.84
    c. 97.72%

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