Usual and Unusual Values. In Exercises, consider a value to be unusual if its z score is less than −2 or greater than 2.

IQ Scores The Wechsler Adult Intelligence Scale measures IQ scores with a test designed so that the mean is 100 and the standard deviation is 15. Consider the group of IQ scores that are unusual. What are the z scores that separate the unusual IQ scores from those that are usual? What are the IQ scores that separate the unusual IQ scores from those that are usual?

Answer:

Step 1 of 1

Here, Unusual values are below 2 standard deviation about the mean or above 2 standard deviation about the mean.

Z scores of –2 and 2.

A z score of –2 means a score of x = 100 - 2(15)

= 70

A z score of +2 means a score of x = 100 + 2(15)

= 130.

.