Unit 5 L-3 Math 8
Aim: Understand that a straight line can represent a scatter plot with linear association. Given a linear
model, students write an equation. (8.SP.2)
The Equation of the Line of Best Fit
Exercise 1:
The table below shows Kellie’s scores on her first seven math quizzes. She made a scatter
plot of her scores and then drew a line of best fit.
Quiz #
1
2
3
4
5
6
7
Quiz
Score
81
83.5
85
85
87
88
90
a. What is the y-intercept of Kellie’s line of best fit? ____________
b. Name the two ordered pairs from the table that are on Kellie’s line.
_____________________
____________________
c. Find the slope of the line using the two ordered pairs you named in part b.
d. Write the equation of the line of best fit in slope-intercept form (y = mx + b).
2014-2015
Exercise 2:
Which equation most closely represents
the line of best fit for the scatter plot at the right?
!
(b) y = !x + 1
!
!
(d) y = !x + 1
(a) y = !x
!
(c) y = ! x + 4
Exercise 3:
A scatter plot was constructed on the graph below
and a line of best fit was drawn.
What is the equation of the
line of best fit?
Exercise 4:
The scatter plot below shows the profit, by month, for a new company for the first year
of operation. Kate drew a line of best fit, as shown in the diagram.
What is the equation of the line of best
fit?
!
(a) y = !x - 2
!
(b) y = !x - 2
!
(c) y = !x
!
(d) y = !x + 2
2014-2015
Exercise 5:
Use the scatter plot and line of best fit to the right to answer the following questions.
a. How many hours would a student have to study to
get a score of 90?
b. If a student studies for 30 hours, what will their
test scores be?
c. How many hours would a student have to study to
get a score of 70?
d. If a student studies for 15 hours, what will their
test score be?
Exercise 6:
The scatter plot to the right shows the relationship between earnings and rank of
Women’s Tennis players in 2001.
a. Draw a line of best fit for the scatter plot.
b. Kim says the equation of the line of best
fit is y = -2x + 2. Is Kim’s equation a
reasonable estimate of the line of best
fit?
2014-2015
Exercise 7:
The scatter plot to the right shows the salaries of engineers based on years of
experience.
a. What is the equation of
the line of best fit?
Show all work.
b. Using the equation estimate the salary of an engineer that has 30 years of experience.
c. Using the line of best fit, estimate the salary of an engineer that has 30 years of
experience.
d. Do your answers in part b and c match? Why or why not?
e. Using the graph, estimate the years of experience an engineer would have that makes
$85,000.
2014-2015