Pre-Algebra Interactive Chalkboard
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Lesson 8-8
Best-Fit Lines
Example 1 Make Predictions from a Best-Fit Line
Example 2 Make Predictions from an Equation
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.
Year
Land
(million acres)
1980
1985
1990
1995
2000
1039
1012
986
963
943
Answer:
Source: U.S. Department of Agriculture
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 2010. 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
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.
Answer:
Year
Number of
Laptops Sold
1998
1999
2000
2001
215
298
395
430
b. Use the best-fit line to predict the
number of laptops sold in the year 2003.
Sample Answer: about 650
Agriculture The scatter plot
shows the number of milk cow
operations in New Mexico from
1975 to 1995. 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).
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.
Step 3 Write the equation.
Slope-intercept form
Replace m with –60
and b with 2100.
Answer:
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
Temperature The scatter
plot shows the heating bill
for the month of January for
different size houses.
a. Write an equation in slopeintercept form for the bestfit line.
Sample Answer:
b. Predict the heating bill for a
house that is 4100 square
feet in size.
Sample Answer: about $308.31
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 www.pre-alg.com/extra_examples.
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