Systems of Equations
Cell Phone Dilemma
Description
In this activity students will learn to:
1. Make Comparisons.
2. Determine a function rule.
3. Analyze data.
Contents
Pages
Student worksheets
2-3
Expected Outcomes
Students will



Review Graphing Equations
Determine the solution for a system of equations – Using a graph or table
Analyze data
NCTM Standards 2000
Algebra
Geometry
© Dr. D. Carluccio, 2006
Representation
Communication
Worksheet
Your parents want to reward you for receiving all A’s on your report card. They agree to
purchase a cell phone for you, but you must find the best plan. You narrow your search
to two plans that include a free phone and the cost per minute.
Cell Phone Company
No Dropped Calls
Text Message Today
Phone Plans
$19.95 Monthly Service fee; plus 10
cents per minute
No Service fee; plus 15 cents per minute
Answer the following questions.
1. How will you solve this problem? Explain the reason you chose that method.
2. If you use 100 minutes, which plan is best? Why is it best?
3. If you use 250 minutes, which plan is best? Why is it best?
4. If you use 500 minutes, which plan is best? Why is it best?
5. How many minutes would you have to use for both plans to be equal?
© Dr. D. Carluccio, 2006
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6. Develop an equation in the slope-intercept form (y=mx+b) for each plan.
7. Using your graphing calculator, graph each equation.
To enter the equations into the graphing calculator follow the directions below.
Press y=
Highlight y1=
Type in the first equation
Press ENTER
In y2= Type in the second equation
Press ENTER
Press ZOOM
Highlight 6:ZStandard
Press ENTER
8. Only the graph of one equation is visible. Explain why. What can you do to have
both graphs visible?
9. Using the trace feature or the table set feature of your graphing calculator, check
your answers for examples 1-5.
10. Based on your findings, which plan would you choose? Justify your answer.
© Dr. D. Carluccio, 2006
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Teacher Notes and Solutions
1. Answers will vary – possibilities include using a table of values, guess and check,
and graphically.
2. Text Message Today. Your bill would be only $15.00 and the bill for No
Dropped Calls would be $29.95.
3. Text Message Today. Your bill would be only $37.50 and the bill for No
Dropped Calls would be $44.95.
4. No Dropped Calls. Your bill for would be only $69.95 and the bill for Text
Message Today would be $75.00.
5. 399 minutes.
6. No Dropped Calls - y = .10x + 19.95
Text Message Today - y = .15x
7. Check students’ calculators.
8. They should see that changing the size of the window would accommodate the
graphs.
9. Check their work.
10. Answers will vary. You want them to see that it depends on how many minutes
you will use monthly.
© Dr. D. Carluccio, 2006
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