In this lesson, students apply their understanding of proportional relationships to solve an open-ended, real-world problem—whether baths or showers use more water. The Warm-up orients students to thinking about quantifying a rate of water flow. Then students brainstorm what they would need to know in order to solve the problem. They make assumptions about the situation and then seek out resources to help them answer the question. As students work to determine relevant quantities and conditions, make approximations, and apply what they know to analyze relationships and draw conclusions, students practice modeling with mathematics (MP4).

Preferably, students work on their own to find values to aid in their solutions. For example, sizes of typical bath tubs are usually listed on websites for hardware stores that carry baths for installation. If these resources are unavailable, the teacher can share some typical ranges or reasonable estimates.

The last activity is optional because it provides an opportunity for additional practice graphing a proportional relationship.