Grade 8 · Linear Relationships

Phone Plan Showdown

Students become consumer advocates, compare competing phone plans, identify break-even points, and make evidence-based recommendations for different customers.

65 minutesConsumer mathSmall groupsLow prep

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Everything needed to teach tomorrow

This is a complete classroom package—not an outline. Preview every component below, then download the editable and printable files.

Teacher GuideScript, timing, questions, misconceptions, and differentiation. Word and PDF.

Student WorkbookWarm-up, tables, graphs, profiles, and written recommendation. Word and PDF.

Complete Answer KeyTables, equations, break-even points, and sample reasoning. PDF.

Assessment PackExit ticket, rubric, observation checklist, and homework. PDF.

Printable CardsPlan cards, customer profiles, vocabulary, and graph pages. PDF.

Preview the actual pages

Teacher Guide — actual lesson script

Essential question: How can equations, tables, and graphs help consumers make smart financial decisions?

Learning target: I can represent phone-plan costs with equations, tables, and graphs and use those representations to recommend the best plan.

0–5 min

Warm-up: What do the numbers mean?

Teacher says: “A company advertises a plan using the equation y = 6x + 25. Without calculating anything yet, what might 6 and 25 mean?”

Expected responses: $6 per gigabyte and a $25 monthly fee. Ask students which quantity changes and which stays constant.

5–12 min

Hook: The cheapest-looking plan

Display three advertisements: “Only $20/month,” “Just $5 per GB,” and “Unlimited savings.” Students vote for the plan they believe is cheapest and explain what information is missing.

Ask: “Why might a company emphasize one number and hide another?”

12–22 min

Model Plan A

Plan A charges a $20 monthly fee plus $8 per GB. Build the table for 0, 2, and 5 GB. Write y = 8x + 20. Plot the y-intercept first, then use the rate of change.

Think aloud: “Even if I use no data, I still pay $20. Every additional gigabyte adds $8.”

22–42 min

Team investigation

Teams receive three actual plan cards:

Plan A: $20 monthly fee + $8/GB
Plan B: $35 monthly fee + $5/GB
Plan C: $50 monthly fee + $3/GB

Students complete tables, equations, and graphs, then identify when each plan becomes the best value.

42–55 min

Customer recommendation challenge

Each team receives one customer profile and prepares a recommendation supported by a calculation, graph evidence, and an explanation of slope and intercept.

55–62 min

Math congress

Compare recommendations. Highlight that different plans can be best for different customers. Connect the intersections to equal-cost situations.

62–65 min

Exit ticket

A plan costs $15 monthly plus $7 per GB. Students write the equation, calculate 9 GB, and explain the slope.

Common misconceptions and teacher responses

“The lowest monthly fee is always cheapest.” Ask students to calculate costs at 2 GB and 20 GB.
Students reverse slope and intercept. Return to the language “starts at” and “adds each time.”
Students treat an intersection as the same data usage. Clarify that the x-coordinate is usage and the y-coordinate is equal total cost.

Phone Plan Showdown — Student Workbook

Name: ____________________ Date: ____________

Part 1: Compare the plans

Data Used	Plan A 20 + 8x	Plan B 35 + 5x	Plan C 50 + 3x
0 GB	$20	$35	$50
2 GB	_____	_____	_____
5 GB	_____	_____	_____
8 GB	_____	_____	_____
10 GB	_____	_____	_____
15 GB	_____	_____	_____

Part 2: Write each equation

Plan Ay = __________

Plan By = __________

Plan Cy = __________

Part 3: Customer profiles

Emma

Uses 3 GB and wants to spend less than $60.

Recommendation: __________

Evidence: ____________________

Alex

Uses 18 GB each month.

Recommendation: __________

Evidence: ____________________

Family Account

Uses 42 GB total. Find the annual savings.

Recommendation: __________

Evidence: ____________________

Written recommendation

I recommend __________________ because ________________________________________________.

The slope means __________________________________________________________________.

The y-intercept means ______________________________________________________________.

Teacher Answer Key

Data Used	Plan A	Plan B	Plan C
0 GB	$20	$35	$50
2 GB	$36	$45	$56
5 GB	$60	$60	$65
8 GB	$84	$75	$74
10 GB	$100	$85	$80
15 GB	$140	$110	$95

Equations: Plan A: y = 8x + 20; Plan B: y = 5x + 35; Plan C: y = 3x + 50.

Break-even points: A and B are equal at 5 GB and $60. B and C are equal at 7.5 GB and $72.50. A and C are equal at 6 GB and $68.

Profiles: Emma should choose Plan A ($44). Alex should choose Plan C ($104 versus $125 and $164). At 42 GB, Plan C is $176/month and saves $828 annually compared with Plan B and $2,160 annually compared with Plan A.

Exit Ticket

A phone plan costs $15 each month plus $7 per GB. Write an equation.
Calculate the total cost for 9 GB.
Explain what the slope represents.
Would this plan cost more or less than Plan B at 9 GB? Show evidence.

Answer: y = 7x + 15; $78; slope is the cost added per gigabyte; Plan B costs $80, so this plan is $2 less.

Recommendation Rubric

Criterion	4 — Strong	3 — Proficient	2 — Developing	1 — Beginning
Mathematical accuracy	All calculations and representations are correct.	Minor error that does not alter recommendation.	Several errors affect reasoning.	Work is mostly incomplete or inaccurate.
Evidence	Uses equation, graph, and table evidence.	Uses two forms of evidence.	Uses one incomplete form.	Recommendation lacks evidence.
Interpretation	Clearly explains slope, intercept, and intersection.	Correctly explains two concepts.	Explanation is partly correct.	Concepts are confused.

Printable classroom resources

Plan A Card$20 monthly fee + $8 per GB

Plan B Card$35 monthly fee + $5 per GB

Plan C Card$50 monthly fee + $3 per GB

Customer Profile CardsEmma, Alex, family, traveler, and budget-conscious user.

Vocabulary CardsSlope, y-intercept, intersection, break-even point, rate of change.

Graphing PageCoordinate grid scaled for 0–20 GB and $0–$180.

Phone Plan Showdown Complete Teaching Kit
Teacher guide, student workbook, answer key, assessments, and printables.

Download complete kit