Making Predictions from Scatterplots
Scatterplot Sort
Cut along the dotted lines.
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Supporting STAAR Achievement: Algebra 1
Name: _________________________________
Making Predictions from Scatterplots
Scatterplots
Complete the concept map by filling in the boxes and drawing in points to show each type of
correlation.
My definition:
How are they
used?
Scatterplot
What does the graph look
like?
Positive Correlation
(Positive Trend)
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Negative Correlation
(Negative Trend)
No Correlation
Supporting STAAR Achievement: Algebra 1
Name: _________________________________
Making Predictions from Scatterplots
Tongue Tied
One person will say the tongue twister while the other records how much time is needed to say the
tongue twister. Your teacher will tell you how many times to say the tongue twister.
Sally sells sea shells by the sea shore.
But if Sally sells sea shells by the sea shore,
then where are the sea shells Sally sells?
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Supporting STAAR Achievement: Algebra 1
Making Predictions from Scatterplots
Number Cards
Numbers can be repeated for classes larger than 30.
1
4
5
6
8
2
4
6
7
10
2
4
6
7
10
1
4
5
6
8
2
4
6
7
10
2
4
6
7
10
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Supporting STAAR Achievement: Algebra 1
Name: _________________________________
Making Predictions from Scatterplots
Tongue Twister Trend Line
Use the data for the class to create a scatterplot for the tongue twister. Make sure to label and
scale the axes.
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Supporting STAAR Achievement: Algebra 1
Name: _________________________________
Making Predictions from Scatterplots
Analyzing the Results
Part 1
Use the graph you created to answer the following questions.
1. As the number of times the tongue twister was said increased, what happened to the total
time?
2. As the total time increased, what happened to the number of times the tongue twister was
said?
3. Does there appear to be a relationship between the total time and number of times the tongue
twister was said? If so, how would you describe the relationship?
4. What type of trend, if any, is depicted by this scatterplot?
Part 2
What if . . .
I want to make a reasonable prediction about the total time of any number of times the
tongue twister is said.
Follow the directions below to draw a trend line to approximate the pattern. The trend line will
help you make good predictions about the total time.
1. Use two pieces of linguine to enclose all of the points on your graph. Be sure to position your
linguine as close to the outer points as possible. (You do not have to keep your linguine lines
parallel.)
2. Use a ruler to draw a line that is halfway between your two linguine lines. This line is called the
trend line.
3. Use the trend line drawn to predict the total time for a person who said the tongue twister
7 times. What is your prediction? Why?
4. Select two points on the line. Write the coordinates of the two points below.
(_____, _____) and (_____, _____)
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Supporting STAAR Achievement: Algebra 1
Making Predictions from Scatterplots
5. What is the slope of your trend line?
6. How are the slope of the trend line and the type of trend for this data related?
7. Write the equation of your trend line.
8. Using the equation you have written, predict the total time for a person to say the tongue
twister 7 times. How does this value compare to the value determined from the graph?
9. Using the equation you have written, predict the total time for a person to say the tongue
twister 25 times. Do you think that is reasonable? Why or why not?
10. Using the equation you have written, predict the total time for a person to say the tongue
twister 2 times. Do you think that is reasonable? Why or why not?
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Supporting STAAR Achievement: Algebra 1
Name: _________________________________
Making Predictions from Scatterplots
Drawing a Trend Line Hints*
Hint for Part 2 Question 5:
1. Write the coordinates of the two points you selected in Question 4 below.
(
,
) and (
,
)
2. Determine the Slope:
Slope=
y y2  y1


x x2  x1




(fraction)
(decimal)
Hint for Part 2 Question 7:
Choose one of the methods shown below to write the equation of the trend line.
Writing an Equation
Using Slope-Intercept Form
Determining the y-intercept
Using the slope found from the two points,
substitute the x- and y-value from one of the
ordered pairs into the slope-intercept equation
and solve for b.
y  mx  b
Writing an Equation
Using Point-Slope Form
Using the slope found using the two points,
substitute the x- and y-value from one of the
ordered pairs into the point-slope form of the
equation.
y  y1  m( x  x1 )
y

(x 
)
____  ____  _____   b
____=_____ + b
____= b
Writing the Equation
Use the slope and y-intercept and write the
equation for the trend line in slope-intercept
form.
y = ____x + ____
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Supporting STAAR Achievement: Algebra 1
Name: _________________________________
Making Predictions from Scatterplots
Making Predictions Using Scatterplots Notes Page
For each scatterplot below, identify the type of correlation shown, if any, and sketch a trend line.
Summarize the key points from the discussion below.
Correlation . . .
A trend line . . .
Making predictions with the graph of the
trend line:
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Making predictions with an equation for the
trend line:
Supporting STAAR Achievement: Algebra 1
Name: _________________________________
Making Predictions from Scatterplots
Coffee Shop Sales
Maurice and Beatrice opened a new store called The Trendy Café. Their goal is to reach a profit of
$25,000 in their 30th month of business. The table and scatterplot below represent the profit in
thousands of dollars, p, that they made during the first 12 months.
The Trendy Café Profits
Months, t
Profit in Thousands
of Dollars, p
1
2
3
4
5
6
7
8
9
10
11
12
3.5
3.0
4.0
5.5
7.0
6.5
7.5
7.0
7.5
8.0
9.0
8.5
Profit (in Thousands of Dollars)
The Trendy Café Profits
Months
1. Draw a trend line for the data.
2. Determine the equation for the trend line.
3. What does the slope of the trend line mean in this situation?
4. If their profit continues along the trend line, predict whether Maurice and Beatrice will reach
their goal in the 30th month of business. Justify your answer.
© Region 4 Education Service Center
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Supporting STAAR Achievement: Algebra 1
Name: _________________________________
Making Predictions from Scatterplots
Coffee Shop Sales*
Maurice and Beatrice opened a new store called The Trendy Café. Their goal is to reach a profit of
$25,000 in their 30th month of business. The table and scatterplot below represent the profit in
thousands of dollars, p, that they made during the first 12 months.
The Trendy Café Profits
Months, t
Profit in Thousands
of Dollars, p
1
2
3
4
5
6
7
8
9
10
11
12
3.5
3.0
4.0
5.5
7.0
6.5
7.5
7.0
7.5
8.0
9.0
8.5
Profit (in Thousands of Dollars)
The Trendy Café Profits
Months
1. What does the ordered pair (12, 8.5) represent in this situation?
2. Draw a trend line for the data.
3. Select two points on the trend line.
(
,
) and (
,
)
4. Use the two points to determine the slope of the trend line.
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Supporting STAAR Achievement: Algebra 1
Making Predictions from Scatterplots
5. What does the slope of the trend line mean in this situation?
6. Determine the y-intercept for the trend line.
7. Determine the equation for the trend line.
8. If their profit continues along the trend line, predict whether Maurice and Beatrice will reach
their goal in the 30th month of business. Justify your answer.
© Region 4 Education Service Center
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Supporting STAAR Achievement: Algebra 1
Name: _________________________________
Making Predictions from Scatterplots
Evaluate: Scatterplots
Miles driven
1. A scatterplot shows the number of miles driven versus the gallons of gasoline remaining in the
gas tank of a car. Which correlation best describes the relationship shown on the scatterplot?
Gallons of gasoline
A
Constant correlation
B
Positive correlation
C
Negative correlation
D No correlation
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Supporting STAAR Achievement: Algebra 1
Making Predictions from Scatterplots
2. Shelia collected data on ticket sales for the homecoming dance.
Number of Tickets Sold
Ticket Sales
Day Number of Ticket Sales
If she plots the data on the scatterplot shown above, which equation best models the trend line
for this data?
A
y 
9
x  24
2
B
y
9
x  24
2
C
y 
2
x  24
9
D
y 
2
x  24
9
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Supporting STAAR Achievement: Algebra 1
Making Predictions from Scatterplots
3. Students in a group of chess teams submitted data about hours of team practice and the
number of matches the team won. The graph shows the results of the data. Based on the data,
if a team practices 4.5 hours per week next year, which is the best estimate of the number of
chess matches a team could expect to win?
Matches Won
Chess Team Practice
Hours of Weekly Practice
A
22
B
19
C
14
D 12
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Supporting STAAR Achievement: Algebra 1
Making Predictions from Scatterplots
4. The scatterplot below shows the algebra grades and the number of absences of different
students for the first semester.
Algebra Grades
Algebra Grades
Number of Absences
Which of the following is the best interpretation of this scatterplot?
A
As the number of absences increase, algebra grades stay the same.
B
Students who have fewer absences seem to have higher algebra grades.
C
Students who have the most absences seem to have higher algebra grades.
D As the number of absences decrease, algebra grades stay the same.
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Supporting STAAR Achievement: Algebra 1