Math Lesson - The Cell Phone

Outcomes or Learning Goals

The story The Cell provides an opportunity for students to think about how impulsive purchasing

decisions can impact finances, and to consider the impact of having a cell phone contract. The story

supports issues of money management as well as budgeting. The related math problems invite

students to compare two cell phone plans through examples of different usage.

Grade Level

MAT1LZ – Locally Developed Math grade 9

MAT2LZ – Locally Developed Math grade 10

Context & Rationale

In the book The Cell Phone we meet Nabi, who buys a new cell phone from a friend and wants to cancel his

current cell phone plan. The context helps students understand the benefits and negatives of having a cell

phone contract, and the impact of the contract terms. Students learn that by comparing two or more cell

phone plans to better understand the cost of usage supports their ability to make purchasing decisions and

to manage their money.

Related Topics/Units

• solve problems involving money drawn from everyday situations (Gr. 9, 10)

• solve problems drawn from everyday situations involving ratio/rate (Gr. 9)

• solve problems involving the calculation of rates drawn from a variety of everyday contexts and from

familiar social issues (Gr. 10)

• calculate rates in activities drawn from their experiences (Gr. 9, 10)

• read, interpret and explain orally and in writing data displayed in simple tables and graphs (Gr. 9, 10)

• communicate information about proportional reasoning (Gr. 9)

• verbalize their observations and reflections and reflections regarding proportional reasoning and ask

questions to clarify their understanding (Gr. 9, 10)

• communicate, orally and in writing, the solutions to proportional reasoning problems and the results of

investigations, using appropriate terminology, symbols and form (Gr. 9)

• explain their reasoning used in problem solving and in judging reasonableness (Gr. 9, 10)

• develop, select, and apply problem-solving strategies while posing and solving problems (Gr. 9)

Number Sense and Numeration Skills from the Ontario Mathematics Curriculum, Grades 1-8 (2005),

that link well to this lesson and would support the needs of limited prior formal learning students are:

• demonstrate an understanding of simple multiplicative relationships involving whole-number rates,

through investigation using concrete materials and drawings (Gr. 5)

• represent relationships using unit rates (Gr. 6)

For the extension problem:

Algebra concepts from the Ontario Mathematics Curriculum, Grades 1-8 (2005), that link well to this

lesson and would support the needs of limited prior formal learning students are:

• use variables in simple algebraic expressions and equations to describe relationships. (Gr. 6)

• translate phrases describing simple mathematical relationships into algebraic expressions (Gr. 7)

Additional References:

Big Ideas and Questioning K-12: Proportional Reasoning

http://www.edugains.ca/resources/LearningMaterials/ContinuumConnection/BigIdeasQuestioning_Pr

oportionalReasoning.pdf

Paying Attention to Proportional Reasoning, K-12

http://www.edu.gov.on.ca/eng/teachers/studentsuccess/ProportionReason.pdf

Paying Attention to Algebraic Reasoning, K-12

http://www.edu.gov.on.ca/eng/literacynumeracy/PayingAttentiontoAlgebra.pdf

NCTM Illuminations: Resources for Teaching Math

http://illuminations.nctm.org

Lesson Sequence

Part 1 Minds On/Prior Learning

(15 minutes estimated for this section)

What to prepare

Activity

1. Remind students of the book they have read, The Cell Phone.

2. To set the context, ask students:

Who has a cell phone?

What kind of plan do you have (contract vs. pay-as-you-go)?

3. Present the problem: A student is getting his first cell phone. His parents said that

they would contribute $25/month. The student researched two cell phone plans,

and is trying to decide between the two. The two plans are compared in the

following chart.

VOICE Minutes

TEXT Messages

PLAN A

5¢/minute

15¢/message

PLAN B

10¢/minute

5¢/message

Copies of the book

The Cell Phone

4. If you were asked to help this student, what questions would you ask him in

order to help him select a plan? Have students turn and talk to a partner, and then

have students share their questions with the class. (e.g., How often do you text?

How often do you call? Is $25 your budget for the month, or can you go over that

amount? Is there a charge for sending and receiving calls and texts?)

Assessment

For the class in general, note whose questions show understanding of the

information and calculations needed to know which is the more suitable plan.

Part 2 – Work On It

(30 minutes estimated for this section)

Work in small groups - 2 per group.

You have a cell phone budget of $25/month. Thinking about the two cell phone

plans (above), answer the following questions:

1. If you were only interested in texting, how many text messages will you be able

to send with each plan?

2. If you were only interested in using the phone to make calls, how long will you be

able to talk with each plan?

3. If you talk for a total of two hours each month, how many texts will you be able

to send with each plan?

4. Create names for PLAN A and PLAN B that clearly describe the benefits of each

plan.

Extension

Write an equation for each plan to represent the number of text messages (x) and

the number of talk minutes (y) you will be able to use with $25. You should have a

separate equation for each plan.

Activities During Work Period

• Students work with partners and record question, work/thinking, and answer on

chart paper.

• Teacher visits partners to clarify the question they are answering and to see if

they have a strategy to start/continue working on the problem.

• Teacher thinks about which solutions to share in the third part of the lesson, and

the order in which they will be shared. Solutions selected should show a variety of

strategies (and hopefully will include the ratio table).

Blank paper for students

to record thinking and

solution.

Assessment

For each student, observe and document:

- use of multiplicative reasoning

- computational strategies and fluency

- clear representation of the problem and communication of thinking

Part 3 – Conclude & Share Solutions

(20 minutes estimated for this section)

Activity

The solutions selected (2-4) are shared, starting with the simplest strategy and

moving to the most complex. Consider which tools/models/algorithms would best

support the learning of the class. Also, consider clarity of communication when

selecting solutions and order in which to share.

As students share their work, encourage them to discuss how they solved the

problem. You may wish to question the students to focus attention on a particular

aspect of their solution, rather than inviting the student to share their entire

process/solution.

Invite other students to ask questions of the presenters.

At the end of the sharing, highlight key learning by recording it on the whiteboard

or on chart paper. The key learning may be connected to a model or strategy used

to solve the problem, or to the problem itself e.g., an explanation of how to know

which cell phone plan is most suitable.

Ticket Out the Door (Independent Formative Assessment Task )

Students independently respond in their math journals or on a piece of paper:

• Which plan would you choose? Why is this the best plan for you? Explain your

thinking.

• Under what circumstances would you choose the other plan?

Collect and assess.

Assessment

For each student, continue to observe and document:

- use of multiplicative reasoning

- ability to apply and use a model/tool/algorithm

- clear representation of the problem and communication of thinking

Students who found the questions challenging would benefit from using a rate or

ratio table to help them understand how to scale up knowing unit rate, and to help

them organize their calculations.

For more information, and instructional strategies to support students in

understanding how to use a ratio table, refer to:

Minilessons for Early Multiplication and Division, by Catherine Twomey Fosnot.

Minilessons for Extending Multiplication and Division, by Catherine Twomey Fosnot.

Follow up Problems

1. Ask students to solve a similar problem using two other cell phone plans.

2. 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?