Technology for Learning

Making a Good Call

by BOB COULTER

Building kids’ financial literacy is an important but sometimes quite challenging goal. Early in my career I did stock market simulations with sixth graders, but quickly realized that the kids could do the math but had a rather superficial understanding of stocks. Another common strategy—tracking how interest builds up over time—can encourage savings, but today’s rates are hardly encouraging. Also, there is a limited scope of what can be done watching interest compound for a period of years. More promising avenues for investigation can be found if we consider what is meaningful for kids today. Many tween-agers have dreams of having a cell phone, and an increasing number actually do. This can open the door to some interesting, math-rich investiga- tions. Just a few are shared here to start your thinking.

Talk Is Cheap (or Is It?)

A typical cell phone plan in the United States and Canada has a base number of min- utes for a monthly fee, and then a per-minute charge for using more than your monthly allotment. This basic premise can set up teams of investigators to examine who has the best price among the different carriers in your community. This will quickly lead to consideration of “best for whom?” scenarios. A light user might need a plan with few minutes, while a regular talker would need more minutes in the plan to avoid what are usually pretty expensive “extra” minutes. For example, one major cell-phone provider currently offers up to 450 minutes for \$39.99/month with each extra minute costing 45 cents. Questions kids can pursue might include:

• How many minutes of talking per day is that? • What if I talk an average of 20 minutes a day. How much will that cost? Should I upgrade my plan?

More advanced students can look for the break-even point: Exactly how many min-

utes per month is the minimum for when it is better to upgrade to the more expensive plan, which in this case offers 900 minutes for \$59.99? Can your students write a simple algebra equation to represent the costs? In this example, where “m” represents minutes over 450, they could write an equation like: Cost = 39.99 + (m  0.45)

Plugging in different values for “m” will give them

different total costs. At what point is the cost more than \$59.99? A spreadsheet with this equation embedded in it will show the point at which the upgrade makes sense pretty quickly. Other people use a phone where they pay per minute,

with no monthly fee. For whom would this be a better plan? The key point in this strand of inquiry is for your students to come to understand that ideas about the “best deal” depend on each person’s needs and circumstances, and that math helps to answer real-world questions like this.

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