The real life applications of math are hard for teenagers to grasp. "When am I ever going to use this in real life?" is a teenage mantra for a reason, but there are times when your teen will need to use math in real life. One good way to help him see how math affects his life is to have him help you evaluate and choose his cell phone plan.

1. Decide on a budget with your teenager. Now is the time to let your child know how much you're willing to contribute to his cell phone plan and how much you expect him to contribute.

If he's going to contribute, help him figure out how much he can realistically afford, based on his monthly allowance or his after-school job.

Making a spreadsheet with his income and other expenses is a concrete way to see his money management skills. Basically, the equation he's trying to solve looks like this:

weekly income (allowance +job) - weekly expenses (food + gas+clothes+entertainment) = $ for cell phone plan

2. Gather information about his current cell phone plan. Many teenagers already have cell phones, whether they're prepaid or an added line on a family plan. What you need to know about the plan is how much it costs per month and what services are included. If she goes over her minutes, what is the charge per extra minute? Is texting unlimited, or does she have a limit and then a pay-per-text charge?

3. Ask your teenager to track her cell phone usage for a week. This means she will need to keep some sort of notebook or record of how many texts she sent and received, and how many minutes she used on calls.

4. Analyze the data together to see which features your teen uses the most. Then ask him to plug his numbers into a few hypothetical scenarios. Assume the data is the same every week and have him multiply his text messages and phone minutes by four to get an average monthly usage. Then, ask him to compare the cost of two situations in which he can:

a) have unlimited texting for $29.95 per month, or

b) have 550 free text message per month, and each additional text is $0.08

Which plan works better? What if he could add 700 minutes to the plan, and each additional minute is $0.05. Does that change anything?

5. Now, compare for real. Sit at the computer with your teenager and visit one of the many websites--like MyRatePlan.com or LetsTalk.com--that allow you to compare the cost of pre-paid phone plans, family plans and single line plans with a variety of different features. Play around with the numbers of texts and minutes until your teenager finds a plan that looks most like his data. Compare the costs and see which cell phone plan is the best fit for his budget.

Your teenager may still groan about using math in real life, but at least now he'll have a concrete example of how math really comes into play in the real world. And, he may have a new and improved cell phone plan to prove it!