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Pre-Algebra Interactive Chalkboard
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3. Lesson 8-8 Best-Fit Lines
Contents

4. Example 1 Make Predictions from a Best-Fit Line
Example 2 Make Predictions from an Equation
Lesson 8 Contents

5. Agriculture The table shows the amount of land in U. S
Agriculture The table shows the amount of land in U.S. Farms from 1980 to 2000.
Make a scatter plot and draw a best-fit line for the data.
1039
1980
943
2000
963
1995
986
1990
1012
1985
Land (million acres)
Year
Source: U.S. Department of Agriculture
Answer:
Example 8-1a

6. Use the best-fit line to predict the amount of land in the year 2010.
Extend the line so that you can find the y value for an x value of The y value for 2010 is about 892. So, a prediction for the amount of farm land in 2010 is approximately 892 million acres.
Answer: about 892 million acres
Example 8-1a

7. Retail The table shows the number of laptop computers sold at a local computer store from 1998 to 2001.
a. Make a scatter plot and draw a best-fit line for the data.
b. Use the best-fit line to predict the number of laptops sold in the year 2003.
Answer:
Year
Number of Laptops Sold
1998
215
1999
298
2000
395
2001
430
Sample Answer: about 650
Example 8-1b

8. Agriculture The scatter plot shows the number of milk cow operations in New Mexico from 1975 to Write an equation in slope-intercept form for the best-fit line.
Step 1 First, select two points on the line and find the slope. Notice that the two points on the best-fit line are not original data points. We have chosen (15, 1200) and (20, 900).
Example 8-2a

9. Step 2 Next, find the y-intercept.
Definition of slope
Simplify.
Step 2 Next, find the y-intercept.
Slope-intercept form
Replace (x, y) with (15, 1200) and m with –60.
Simplify.
Example 8-2a

10. Step 3 Write the equation.
Slope-intercept form
Replace m with –60 and b with 2100.
Answer:
Example 8-2a

11. Predict the number of milk cow operations in the year 2005.
Write the equation for the best-fit line.
Replace x with 30.
Answer: about 300 milk cow operations
Example 8-2a

12. a. Write an equation in slope- intercept form for the best- fit line.
Temperature The scatter plot shows the heating bill for the month of January for different size houses.
a. Write an equation in slope- intercept form for the best- fit line.
b. Predict the heating bill for a house that is 4100 square feet in size.
Sample Answer:
Sample Answer: about $308.31
Example 8-2b

13. End of Lesson 8

14. Explore online information about the information introduced in this chapter.
Click on the Connect button to launch your browser and go to the Pre-Algebra Web site. At this site, you will find extra examples for each lesson in the Student Edition of your textbook. When you finish exploring, exit the browser program to return to this presentation. If you experience difficulty connecting to the Web site, manually launch your Web browser and go to
Pre-Alg.com

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