Statistics
posted by Larry English .
1. The mean and standard deviation of the grades of a group of students who took an economic exam were 69 and 7, respectively. The grades have a moundshaped distribution. According to the Empirical Rule,
a) Approximately 68% of the grades were between which grade?
b) Approximately what percentage of grades were between 55 and 76?

a. 68% are mean ± 1 SD.
b. Z = (scoremean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportions related to the Z scores (from Z = 2 to +1).