Read this article, which explores various real-world situations where evaluating expressions with one or more variables is required. Then, complete practice problems 1-9 and 26-30. If you need help with problems 1-9, watch the first 2 minutes of the "Variable Expressions" video embedded in the article.

Click http://www.ck12.org/book/CK-12-Basic-Algebra-Concepts/section/1.2/ link to open resource.