Illuminations: Talk or Text

# Talk or Text

 In this lesson, students compare different costs associated with two cell phone plans. They write equations with 2 variables and graph to find the solution of the system of equations. They then analyze the meaning of the graph and discuss other factors involved in choosing a cell phone plan.

### Learning Objectives

 Students will: Compare two cell phone plans through examples of different usage Write equations to model allocation of money for cell phone usage Graph and solve a system of equations Analyze the solution and the meaning of the graph

### Materials

 Computer with Internet access (optional) Information about current cell phone plans (optional) Talk or Text? Activity Sheet Talk or Text? Answer Key

### Questions for Students

 Under what circumstances is each cell phone plan better? [Plan A is better when you talk on the phone more. Plan B is better when you send text messages more.] What does the graph of each equation represent? [combinations of texts and minutes that cost exactly \$25] What does the space underneath the graph of the line represent? [combinations of texts and minutes that cost less than \$25] What does the space above the graph of the line represent? [combinations of texts and minutes that cost more than \$25] Can you use quadrant II, III, or IV? [No, because you cannot have negative minutes or negative text messages.] What other factors might you consider when choosing a cell phone plan? [Answers will vary, but student comments may include activation fees, mobile-to-mobile minutes, weekend or evening minutes, cell phones available, or "extras" like voice mail and ring tones.]

### Assessment Options

 Ask students to solve a similar problem using two other cell phone plans. Ask students to write a journal entry explaining which plan they would choose and why. Under what circumstances would they choose the other plan? Give students the average number of text messages sent and the average number of minutes used by a particular person. Which plan should that person choose? Why? How much money would they save?

### Extensions

 Students can research and compare plans offered by two or more different companies. Have them compare different factors, such as free evening and weekend minutes or cell phones offered from the company, and discuss how these variables would affect their choices. Students can compare individual versus family plans, weighing the benefits and drawbacks of each. Extend the lesson to other types of memberships, such as movie rental programs or gym memberships. Have students compare similarities and differences in features or types of membership categories.

### Teacher Reflection

 Do students understand the meaning of each plan? Were students appropriately challenged? How could you modify the lesson for students at a higher or lower level? Were students able to explain why they would choose a particular plan? Did they demonstrate understanding of the mathematics? Did students have difficulty writing the equations? How could you scaffold this skill?

### NCTM Standards and Expectations

 Algebra 6-8Relate and compare different forms of representation for a relationship. Represent, analyze, and generalize a variety of patterns with tables, graphs, words, and, when possible, symbolic rules. Use symbolic algebra to represent situations and to solve problems, especially those that involve linear relationships. Algebra 9-12Write equivalent forms of equations, inequalities, and systems of equations and solve them with fluencyâ€”mentally or with paper and pencil in simple cases and using technology in all cases.
 This lesson was prepared by Katie Hendrickson as part of the Illuminations Summer Institute.

1 period

### NCTM Resources

 More and Better Mathematics for All Students
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