Question

IQ scores are normally distributed with a mean of 100 and a standard deviation of 15. What percentage of people have an IQ score higher than 66, to the nearest tenth?

Answer 1

We need to find the area under the standard normal curve that is to the right of 66.

Various ways of doing this include the following:

1) Calculator: normalcdf(66, 10000, 100, 15) = 0.988, or 98.8%

2) z-scores (using a published table of z scores)
66 - 100
a) Find the z score corresponding to 66. It is z = -------------- = -2.27
15

b) Find the area under the st. normal curve to the left of z=-2.27 (it is 0.012). Subtract that area from the total area, 1.000. The result will be the answer to this question.