Barbie Bungee Lesson 3

  • Building a Better Barbie Prediction

    Lesson 3 of 3
    8th grade and High School Statistics / Algebra

    45-60 minutes


    Help Barbie make a better prediction for her bungee jump by using a line of best fit and analyzing residuals.



    In Lesson 1, students collected data relating the number of rubber bands attached to Barbie and the lowest point that Barbie's head reaches. A scatter plot was used to make a prediction for the number of rubber bands that would give Barbie the most thrilling jump that still keeps her safe. In Lesson 2, students discovered a method for finding a line of best fit and identified the correlation coefficient (r) as a measure of the strength of the linear relationship. In this lesson, students will use the equation of the line of best fit to create a residual plot. Then they will revise their predictions from Lesson 1.

    Display the data that are at the top of the Lesson 3 Student Activity Sheet.

    “During our measuring day, one of the groups forgot to record their data for 5 rubber bands. Without measuring again, how could we make a good prediction for this value?”

    Students might suggest taking the average of the values for 4 and 6 rubber bands. Another suggestion might be to take a poll of the rest of the groups. Encourage students to think about what we did in the previous lesson. The goal is to realize that the line of best fit would be a good tool to calculate the missing value.


    The activity sheet is intended for students to complete in groups. Prompt students with ideas or questions to check for and deepen student understanding.

    • “How good are the predictions from the line of best fit?”
    • "Why are some of the residuals negative?" (SMP 2)
    • "On the scatterplot, where are all of the points with a negative residual?"
    • "If our linear model is a good model, what should we see in the residual plot?"
    • "Is your line of best fit a good fit for your data? How do you know?"


    Bring the groups back together for a class discussion. Talk through the questions on the Lesson 3 Student Activity Sheet.
    Remind students that one value of the line of best fit is to make predictions.

    Predictions made from x-values within the data set are called interpolations. Predictions made from x-values outside the data set are called extrapolations and may not be as reliable as predictions made using interpolation. Ask students, "Why do you think this is the case?" A potential response may include, "The pattern may not hold true for larger x-values, we know what the pattern is between the two x-values, but are uncertain for x-values outside. For example if you stretch rubber bands too far, they break.”

    A residual plot shows the error in each prediction. Residual values close to 0 indicate the line of best fit will be near the actual data point. Residual values should also be random in nature, some positive, some negative. For example, a curved pattern of residuals may indicate the model is not a good fit.

    The correlation coefficient and the residual plot are two ways to assess the quality of our line of best fit.
    Show the students the applet from Day 2. The applet creates a residual plot.

    Teacher Reflection

    • What questions did you ask students that best helped you to assess their understanding of residuals and residual plots?
    • What questions did you ask students that best helped them to move forward when they were stuck or to deepen their understanding?
    • What misconceptions did your students have related to the topics addressed in this lesson and how did you address those misconceptions?

    Leave your thoughts in the comments below.

    Related Material

    Explore linear regression and residuals using this Geogebra interactive.

    Other Lessons in This Activity

    Lesson 1 of 3
    Students will collect and present data for dropping a Barbie (or other object) from a set height using rubber bands in order to make predictions.
    Lesson 2 of 3
    Find the line of best fit for the Barbie Bungee data, interpret the slope and y-intercept, and understand the correlation coefficient.
  • Comments


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      Would like other activities that could be used as an extension or additional practice for finding a line of best fit and looking a "r" factor.

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  • Essential Question(s)

    • How can we use the equation for the line of best fit to make predictions? How do we know if the line of best fit is making good predictions?


    CCSS, Content Standards to specific grade/standard

    • S.ID.6.a Fit a function to the data; use functions fitted to data to solve problems in the context of the data. Use given functions or choose a function suggested by the context. Emphasize linear, quadratic, and exponential models.
    • S.ID.6.b Informally assess the fit of a function by plotting and analyzing residuals.
    • S.ID.6.c Fit a linear function for a scatter plot that suggests a linear association.

    CCSS, Standards for Mathematical Practices

    • SMP 2 Reason abstractly and quantitatively.
    • SMP 5 Use appropriate tools strategically.

    PtA, highlighted Effective Teaching Practice and/or Guiding Principle CCSS

    • Implement tasks that promote reasoning and problem solving.
    • Use and connect mathematical representations.
    • Facilitate meaningful mathematical discourse.
    • Pose purposeful questions.
    • Elicit and use evidence of student thinking.