Intro to Stats study guide

Question

The question on the study guide is as follows:

IQ scores are normally distributed with a mean of 100 and a standard deviation of 15. Joe has an IQ that is higher than 99% of people. What is Joe's IQ?

Answer 1

The formula for the area under the normal distribution curve is:

 

(Your sample parameter - population mean)/standard deviation

 

You can then look up the answer (which is the number of standard deviations away from the mean) in the z-score table to get the probability of that occurrence.  You can see the z-table at this link: 

http://sixsigmastudyguide.com/z-scores-z-table-z-transformations/

 

(x - 100)/15 = z(.99)

(x - 100) / 15 = 2.33

x - 100 = 35

x = 135