Begin by asking students who has a cell phone. Ask what type of
plan they have, and how they chose it. Discuss different options
provided by plans, rates charged for text messaging, and rates for
voice minutes. Some students may use pre-paid plans, and others may use
a monthly contract. You may want to show a few examples of current
plans offered by cell phone companies.
Tell students that they will be looking at two prepaid plans offered by two different cell phone companies. Distribute the Talk or Text? activity sheet to each student.
Depending on students' ability levels and familiarity with the
concepts, you may want to put students in groups of 2 to 4. Explain to
students that their parents have decided to but them their first cell
phone, and the parents have agreed to prepay $25 each month to be used
for voice minutes and text messaging. Allow students time to look at
the chart and discuss which cell phone plan would be best under which
circumstances before reading through the questions on the activity
Give groups time to complete Questions 1 to 5. Walk around the
room and help students as needed. When they are finished, bring the
whole class together to discuss the answers (found on the Talk or Text? answer key). Students may have found x- or y-values that are fractions or decimals, such as sending 1662/3 text messages for Plan A in Question 1. Ask them what this means. Is it possible to send 1662/3 text messages? Students should realize that you cannot send 2/3
of a text message, so the answer to Question 1 is 166 text messages.
Ensure that everyone has the correct equation and understands what the
equations mean in the context of the problem situation.
Allow groups to complete the remainder of the activity sheet.
Direct students to graph their equations using whichever method they
choose (slope and y-intercept, x/y table, or x and y intercepts). You may also want to discuss the meaning of negative x- and y-values.
Is it possible to send a negative number of text messages or talk on
the phone for negative minutes? Students should realize that only
positive values make sense in this problem, and therefore they should
be graphing in quadrant I only.
When students have finished the activity sheet, lead a whole
class discussion on what they have found out about the phone plans by
answering the questions. Did they choose the plan they thought they
would before working through the activity? Which plan did they choose
and why? Which plan was most popular in the class? You can also create
lists of pros and cons of each plan on the board. Emphasize to students
that there is no right answer to this problem. The best choice for an
individual is based on that person's phone habits. However,
investigating plans mathematically can lead any person to make a
better, more informed decision.