http://www.ck12.org Chapter 7. Organizing and Displaying Data - Basic
7.1 Line Graphs and Scatter Plots
Learning Objectives
- Represent data that has a linear pattern on a graph.
- Represent data using a broken-line graph and represent two sets of data using a double line graph.
- Understand the difference between continuous data and discrete data as it applies to a line graph.
- Represent data that has no definite pattern as a scatter plot.
- Draw a line of best fit on a scatter plot.
- Use technology to create both line graphs and scatter plots.
Introduction
Each year the school has a fund raising event to collect money to support the school sport teams. This year the
committee has decided that each class will make friendship bracelets and sell them for $2.00 each. To buy the
necessary supplies to make the bracelets, each class is given $40.00 as a start up fee. Create a table of values and
draw a graph to represent the sale of 10 bracelets. If the class sells ten bracelets, how much profit will be made?
We will revisit this problem later in the lesson.
When data is collected from surveys or experiments, it can be displayed in different ways; tables of values, graphs,
and box-and-whisker plots. The most common graphs that are used in statistics are line graphs, scatter plots, bar
graphs, histograms, frequency polygons. Graphs are the most common way of displaying data because they are
visual and allow you to get a quick impression of the data and determine if there are any trends in the data. You
have probably noticed that graphs of different types are found regularly in newspapers, on websites, and in many
textbooks.
If we think ofindependentanddependentvariables in terms of the variables in an input/output machine –we can
see that theinputvariable isindependentof anything around it but theoutputvariable is completelydependent
on what we put into the machine. Theinputvariable is thexvariable and theoutputvariable is they(or thef(x))
variable.
If we apply this theory to graphing a straight line on a rectangular coordinate system, we must first determine which
variable is the dependent variable and which one is the independent variable. Once this has been established, the
ordered pairs can be plotted.
Example 1:If you had a job where you earned $9.00 an hour for every hour you worked up to a maximum of 30
hours, represent your earnings on a graph by plotting the money earned against the time worked.
Solution:The dependent variable is the money earned and the independent variable is the number of hours worked.
Therefore, money is on they−axis and time is on thex−axis. The first step is to create a table values that represent
the problem. The number pairs in the table of values will be the ordered pairs to be plotted on the graph.