Lesson objective: Determine the constant of proportionality using division and write equations for a real life situation.

This lesson helps to build procedural skill with determining the constant of proportionality. Equations are used here because it shows how the independent and dependent variable relate to each other. This work develops students' understanding that the constant of proportionality describes how one quantity changes when the other quantity changes by one.

Students engage in Mathematical Practice 8 (Express regularity in repeated reasoning) as they determine the constant of proportionality and interpret how it relates to the independent and dependent variables.

**Key vocabulary:**

- constant of proportionality
- independent variable
- dependent variable

**Special materials needed:**