## Lesson: Adding and Subtracting Equal Amounts

Developing the Concept

When students have begun to grasp the idea that you can keep both sides of an equation equal if you perform the same operation on each side, show them how that balancing process can be used to find a missing number in an equation or solve the equation for a variable.

**Materials: ** overhead projector or chalkboard on which to write

**Preparation: ** Write the equation** n − 3 = 8** on the board or overhead projector.

**Wrap-Up and Assessment Hints**

Students need practice with balancing equations. Assess student progress by asking them to provide five possible solutions to 3 + 12 = . If students can only answer 15, then you know that more work is needed for them to understand the concepts regarding balancing equations. The goal is for students to understand eventually that there are many possibilities, such as 4 + 11, 5 + 10, 6 + 9, 20 − 5, and so on. This will allow you to see if students truly understand the concept of balancing equations. To assess their understanding of variables, provide matching exercises. Have them match equations such as *n *+ 9 = 11 with simplified equations (for example,* n *= 2). You can also have them write equations using variables to model real-life situations you provide.