Lesson #83 Writing the equation of a line of best fit
Do Now: Write the equation of the line that passes through the points (-1, 5) and (2, -4).
(Hint: Find the slope first, then use y = mx + b to find the y-intercept)
1. The scatter plot below shows the relationship between the number of chapters and the total
number of pages for several books.
Scatter Plot of
# of pages and chapters in a book
a) Draw the trend line using the points (5, 50) and (17, 170).
Then write the equation of the trend line.
Step 1: Find the slope.
Step 2: Find the y-intercept using y = mx + b
Step 3: Write the equation slope-intercept form. _____________________
c) Use your equation to predict how many pages
chapters
would be in a book with 26 chapters.
d) Use your equation to predict how many
would be in a book with 320 pages.
2. Annika asks several of her classmates to make a T with their bodies standing
up straight and putting their arms straight out to their sides. She measures
their arm spans and their heights in inches.
a) Make a scatter plot using the data and draw in the trend line that passes through the
points (55, 55) and (65, 65).
b) Do you see any outliers? Why might there be an outlier?
_______________________________________________________________________________
c) Find the equation of the trend line. (Hint: Find the slope first, then use y = mx + b to find the
y-intercept)
d) Using the equation of the trend line, predict the arm span of an individual who is 58 inches tall.
e) Your height in inches _______. Use the equation of the line of best fit to predict your arm span.
Now, You Try! Write the equation of each trend line below using the two points given.
3) Write the equation of the trend line shown below using the points (20, 130) and (30, 125).
4) Write the equation of the trend line shown below using the points (2, 8) and (9, 9.5)