posted by terry .
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
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.