Question

Suppose that grade point averages of undergraduate students at one university have a bell-shaped distribution with a mean of 2.61 and a standard deviation of 0.4. Using the empirical rule, what percentage of the students have grade point averages that are between 2.21 and 3.01?

Answer 1

68%

Explanation:

We start by calculating the z-scores of both

z-score = (x-mean)/SD

for 2.21

z-score = (2.21-2.61)/0.4 = -1

For 3.01

z-score = (3.01-2.61)/0.4 = 0.4/0.4 = 1

So what we want to find is the percentage between -1 SD and 1 SD of the mean

This is the percentage corresponding to the probability

P(-1 < x < 1)

According to the empirical rule, this is a value of;

68.269%