# 12.9: Regression - Textbook Cost (Worksheet)

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- 5118

- Contributed by Barbara Illowsky & Susan Dean
- Statistics at De Anza College
- Sourced from OpenStax

Name: ______________________________

Section: _____________________________

Student ID#:__________________________

*Work in groups on these problems. You should try to answer the questions without referring to your textbook. If you get stuck, try asking another group for help.*

**Student Learning Outcomes**

- The student will calculate and construct the line of best fit between two variables.
- The student will evaluate the relationship between two variables to determine if that relationship is significant.

**Collect the Data**

Survey ten textbooks. Collect bivariate data (number of pages in a textbook, the cost of the textbook).

- Complete the table.
**Number of pages****Cost of textbook** - Which variable should be the dependent variable and which should be the independent variable? Why?
- Graph “pages” vs. “cost.” Plot the points on the graph in Analyze the Data. Label both axes with words. Scale both axes.

**Analyze the Data**

Enter your data into your calculator or computer. Write the linear equation, rounding to four decimal places.

- Calculate the following:
- \(a =\) ______
- \(b =\) ______
- correlation = ______
- \(n =\) ______
- equation: \(\hat{y} =\) ______
- Is the correlation significant? Why or why not? (Answer in complete sentences.)

- Supply an answer for the following senarios:
- For a textbook with 400 pages, predict the cost.
- For a textbook with 600 pages, predict the cost.

- Obtain the graph on your calculator or computer. Sketch the regression line.
**Figure 12.9.1.**

**Discussion Questions**

- Answer each question in complete sentences.
- Does the line seem to fit the data? Why?
- What does the correlation imply about the relationship between the number of pages and the cost?

- Are there any outliers? If so, which point(s) is an outlier?
- Should the outlier, if it exists, be removed? Why or why not?