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 mound-shaped distribution. According to the Empirical Rule,

Question

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 mound-shaped 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?

PsyDAG · Answer

a. 68% are mean ± 1 SD.

b. Z = (score-mean)/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).