### Chapter 9 Review Exercises

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• 21. Confidence Interval for the Population Mean of New York Teacher Salaries

The histogram shows the distribution of the salaries of 75 New York public school teachers. Use the Confidence Interval Calculator and a 95% confidence level to estimate the population mean salary.

• Worked-Out Solution

Using the Confidence Interval Calculator located in Tools, you can obtain the following.

• 95% Confidence Level: The population mean is \$65,467 ± \$1710.99.

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``` __   __    _____     _____    __   __     _____
\ \\/ //  |  ___||  / ____||  \ \\/ //   / ___//
\   //   | ||__   / //---`'   \ ` //    \___ \\
/ . \\   | ||__   \ \\___      | ||     /    //
/_//\_\\  |_____||  \_____||    |_||    /____//
`-`  --`  `-----`    `----`     `-`'   `-----`

```
• 22. Confidence Interval for the Population Mean of New York Teacher Salaries

The histogram shows the distribution of the salaries of 75 New York public school teachers. Use the Confidence Interval Calculator and a 99% confidence level to estimate the population mean salary.

These comments are not screened before publication. Constructive debate about the information on this page is welcome, but personal attacks are not. Please do not post comments that are commercial in nature or that violate copyright. Comments that we regard as obscene, defamatory, or intended to incite violence will be removed. If you find a comment offensive, you may flag it.

```           _    _                ___      ______
____    | || | ||     ___     / _ \\   /_____//
|    \\  | || | ||    /   ||  / //\ \\  `____ `
| [] ||  | \\_/ ||   | [] || |  ___  || /___//
|  __//   \____//     \__ || |_||  |_|| `__ `
|_|`-`     `---`       -|_|| `-`   `-`  /_//
`-`                     `-`             `-`
```
• 23. Bias in a Presidential Approval Survey

Explain why the sample may be biased. Then explain how to find an unbiased sample.

A politically conservative magazine wants to estimate the percent of U.S. adults who approve of the job the president is doing. The magazine sends the survey to readers on its mailing list.

• Worked-Out Solution

The sample may be biased because conservative people would have a positive opinion of a conservative president and a negative opinion of a liberal president. To find an unbiased sample, the magazine should send the survey to a random sample of people.

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```  _____      ___    __    __     ___     _____
|__  //    / _ \\  \ \\ / //   / _ \\  |  __ \\
/ //    | / \ ||  \ \/ //   | / \ || | |  \ ||
/ //__   | \_/ ||   \  //    | \_/ || | |__/ ||
/_____||   \___//     \//      \___//  |_____//
`-----`    `---`       `       `---`    -----`

```
• 24. Bias in an Election Survey

Explain why the sample may be biased. Then explain how to find an unbiased sample.

A pollster wants to determine the percent of registered voters who voted for the Republican candidate in an election. The pollster conducts an exit poll in a primarily Republican neighborhood.

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```  ____      _____                ___       _____
|  _ \\   |  ___||     ___     / _ \\    / ___//
| |_| ||  | ||__      /   ||  | / \ ||   \___ \\
| .  //   | ||__     | [] ||  | \_/ ||   /    //
|_|\_\\   |_____||    \__ ||   \___//   /____//
`-` --`   `-----`      -|_||   `---`   `-----`
`-`
```
• 25. Sample Size for a Voting Survey

You work for a political campaign. You want to estimate the percent of registered voters who plan to vote for your candidate. Use the Sample Size Calculator. Choose a 90% confidence level and a 2% margin of error. How many people should you survey to obtain reliable results?

• Worked-Out Solution

Using the Sample Size Calculator located in Tools, you can see that you need to survey 1692 people to obtain reliable results.

These comments are not screened before publication. Constructive debate about the information on this page is welcome, but personal attacks are not. Please do not post comments that are commercial in nature or that violate copyright. Comments that we regard as obscene, defamatory, or intended to incite violence will be removed. If you find a comment offensive, you may flag it.

``` _    _     ______   _____     _    _     _  __
| || | ||  /_   _// |  __ \\  | || | ||  | |/ //
| || | ||   -| ||-  | |  \ || | || | ||  | ' //
| \\_/ ||   _| ||_  | |__/ || | \\_/ ||  | . \\
\____//   /_____// |_____//   \____//   |_|\_\\
`---`    `-----`   -----`     `---`    `-` --`

```
• 26. Biased Question about Whether a Senator Should Resign

Determine which question could produce biased results. Explain.

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```   _____    ______    _____    __   __    ____