
Concept explainers
For Problems 1 and 2, (a) determine the null and alternative hypotheses, (b) explain what it would
1. Credit-Card Debt According to creditcard.com, the mean outstanding credit-card debt of college undergraduates was $3173 in 2010. A researcher believes that this amount has decreased since then.
a.

Answer to Problem 1RE
Null hypothesis:
Alternative hypothesis:
Explanation of Solution
Given info:
In 2010, a researcher believed that the mean credit card debt of college graduates has been decreased.
Justification:
Null hypothesis:
That is, the mean outstanding credit card debt of college graduates has not been decreased since 2010.
Alternative hypothesis:
That is, the mean outstanding credit card debt of college graduates has been decreased since 2010.
b.

Explanation of Solution
Type I error: Rejecting the null hypothesis, when it is actually true.
A type-I error is made by concluding the evidence as “the mean outstanding credit card debt of college graduates has been decreased since 2010”. But in reality, the actual mean outstanding credit card debt of college graduates has not been decreased since 2010.
c.

Explanation of Solution
Type II error: Fail to reject the null hypothesis, when it is false.
A type-II error is made by concluding the evidence as “the mean outstanding credit card debt of college graduates has not been decreased since 2010”. But in reality, the actual mean outstanding credit card debt of college graduates has been decreased since 2010.
d.

To state: The conclusion based on the results of the test.
Answer to Problem 1RE
The conclusion is that, “there is no sufficient evidence to infer that the mean outstanding credit card debt of college graduates has been decreased since 2010”.
Explanation of Solution
Conclusion:
From the given information, the null hypothesis is not rejected. Thus, there is no enough evidence to infer that the mean outstanding credit card debt of college graduates has been decreased since 2010.
e.

To state: The conclusion based on the results of the test.
Answer to Problem 1RE
The conclusion is that, “there is sufficient evidence to infer that the mean outstanding credit card debt of college graduates has been decreased since 2010.
Explanation of Solution
From the given information, the null hypothesis is rejected. Thus, there is enough evidence to infer that the mean outstanding credit card debt of college graduates has been decreased since 2010.
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Chapter 10 Solutions
MyLab Statistics with Pearson eText -- Standalone Access Card -- for Fundamentals of Statistics
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