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# 6.3: Finding a Line of Best Fit

Difficulty Level: At Grade Created by: CK-12

This activity is also intended to supplement Algebra I, Chapter 5, Lesson 5.

In this activity, you will explore:

• Creating a scatter plot representing resting heart rates versus age.
• Graphing vertical and horizontal lines to show \begin{align*}Q1\end{align*} and \begin{align*}Q3\end{align*} for both the ages and the heart rates.
• Using the vertices of the \begin{align*}Q1\end{align*} and \begin{align*}Q3\end{align*} lines to calculate a line of best fit and graph it.

## Problem 1 - Entering the Data

Enter the 21 data points shown in the screens below in the AGE and RHR lists.

Plot this data as a scatter plot.

## Problem 2 - Answer the Questions

• What are \begin{align*}Q1\end{align*} and \begin{align*}Q3\end{align*} of the ages? Graphs these as horizontal lines.
• What are \begin{align*}Q1\end{align*} and \begin{align*}Q3\end{align*} of the heart rates? Graph these as vertical lines.
• Where do these lines intersect? Write the coordinates of the four points.
• Identify the diagonal across the center rectangle that follows the direction of the points. What two intersection points does it connect?
• Use these two points to write the equation for the line that will form the diagonal using the point-slope form.

## Problem 3 - Graph the Equation

Using the information from Problem 2, graph the equation of the line.

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