[sigmagirl2000]

linear equations can be used in simple applications like "I have to pay my cell phone bill. It costs $50 a month, then $.10 for every text I go over however many are allotted in the plan." The .10 would be your slope, and the $50 would be your y-intercept. You can use those to graph and determine how much you will pay per month based on the number of texts over your plan you use, etc. You can compare your own cell phone plan to other plans to determine if you have the best plan based on your usage and needs (by solving a system of equations.) etc. I don't know. As a math teacher, I constantly apply what we are doing in classes to teens.... if you want more ways, let me know and I'll pay attention to the things that fall out of my mouth during class when I get "why do we need this?" questions. (because the responses are spontaneous, and without any thought)