This lesson parallels the previous one, except the focus is on situations that lead to equations of the form Tape diagrams are used to help students understand why these situations can be represented with equations of this form, and to help them reason about solving equations of this form. Students also attend to the meaning of the equation’s solution in the context (MP2). Note that we are not generalizing solution methods yet; just using diagrams as a tool to reason about solving equations.

In the last activity of this lesson, students distinguish between equations of the form  and . They consider two stories and corresponding diagrams and write equations to represent them. They use these representations to find an unknown value in the story. However, the Cool-down focuses on an equation of the form .