Chapter 8, Problem 25E

(a)

To determine

To explain should you choose to take this retest.

Answer to Problem 25E

We should not take retest.

Explanation of Solution

It is given that people who claim to “have ESP” participate in a screening test in which they have to guess which of several images someone is thinking of. We took the test. We scored two standard deviations above the mean and friend scored one standard deviation below the mean. So, the researcher offer everyone the opportunity to take the retest. Thus, we should probably not take the retest because your score is better than about $97.5\%$ of people, assuming scores follow the normal model. Your next score is likely to be closer to the mean.

(b)

To determine

To explain to your friend what his decision should be and why.

Answer to Problem 25E

The friend should retake the test.

Explanation of Solution

It is given that people who claim to “have ESP” participate in a screening test in which they have to guess which of several images someone is thinking of. We took the test. We scored two standard deviations above the mean and friend scored one standard deviation below the mean. So, the researcher offer everyone the opportunity to take the retest. Thus, the friend should probably retake the test, as his score is better than only about $16\%$ of people. His score is likely to be closer to the mean.