Ask students to pay special attention to the units used to define the x-axis and y-axis on their graph in question four. Depending on the knowledge of the students, the instructor may need to spend some time reminding students of appropriate division of the x-axis and y-axis in applications.
Assessment of this activity may be done by the instructor walking around the classroom and providing guidance when needed. A Phone Bill Worksheet Key is provided to allow for a quick check of student progress.
This activity is a modification of a project found in "Interesting Data Analysis Problems for the TI-82" by Tom Reardon.