Question

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:
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

Answer 1

Normally distributed means that median = mean = mode. Median = 50th percentile. Does that give you answer to a?

b. 50 + .5(68) = ?%
d. 50 - .5(68) = ?

Use similar procedures to answer the rest of the problems.

Answer 2

Normally distributed means that median = mean = mode. Median = 50th percentile. Does that give you answer to a?