Scores of adults aged 60 to 64 on a common IQ test are approximately Normally distributed with mean 90 and standard deviation 15.
About what percent of the population of adults aged 60 to 64 have an IQ lower than 60?
A) 90 percent
B) 20 percent
C) 16 percent
D) 10 percent
E) 2.5 percent

Question

Quizplus · Accepted Answer

Using the properties of the normal distribution, a score of 60 is 2 standard deviations below the mean (90 - 2*15 = 60). Approximately 2.5% of the population falls below 2 standard deviations from the mean in a normal distribution.

Scores of Adults Aged 60 to 64 on a Common