statistics
posted by Ab .
Assume that a set of test scores is normally distributed with a mean of 100 and a standard deviation of 20. Use the 689599.7 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

Z = ± 1 = ± 34% = 68%
Z = ± 1.96 (about 2) = ± 47.5% = 95%
Z = ± 2.96 (about 3) = ± 49.87% = 99.7%
This information should help you to find your own answers. 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?