Question

Given that the general population is normally distributed on a standard scale measuring math aptitude with Mean = 50 (s.d. = 10), approximately what percentage of the population has a math aptitude score between 40 and 60?

Answer 1

You need to find the z-score

(40 - 50)/10 = z

(60 - 50)/10 = z

So, you are looking for -1 and +1 standard deviations.

Find the area between -1 and +1 standard deviation by using a z-table or else by using the 65.. etc, rule.

Answer 2

68.2%