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Assume that a set of test scores is normally distributed with a mean of 100 and a standard deviation of 20. Use the 68-95-99.7 rule to find the following quantities:
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 = (score-mean)/SD

    Find the values and then use the rule, remembering that the percentages are on both sides of the mean.

  • statistics -

    Help me know if I am on the right track, I got:
    a-50%, b-120/150 or 4/5, c- 93.3%, d-53.3%, e-60/150 or 2/5, f- 20%

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