# Lesson 19

Trash Talk

### Lesson Purpose

The purpose of this lesson is to find areas by multiplying side lengths in situations where the side lengths are two- or three-digit numbers.

### Lesson Narrative

In previous lessons, students have learned to use the standard algorithm to multiply whole numbers including a three-digit and a two-digit number. The purpose of this lesson is to apply those techniques to a situation involving areas related to the Great Garbage Patch. The measurements are given in kilometers so students review, in the first activity, how long a kilometer is. Then, students calculate the area of states to get a sense for the size of the Great Garbage Patch. One of these calculations is a product of two three-digit numbers. After this brief interlude solving problems about area, students return to volume for the final two lessons. The area calculations for the states showed the importance of estimation since finding the exact products requires careful calculations whereas a quick estimate shows that the area of New Mexico is less than the area of the Great Garbage Patch. This estimation builds on student learning from the previous activity and then next two lessons combine estimation, volume, and trash.

• Representation
• MLR8

Activity 1: Square Kilometers

### Learning Goals

Teacher Facing

• Use multiplication to solve problems about the area of the Great Garbage Patch.

### Student Facing

• Let’s multiply to solve problems about the area of the Great Garbage Patch.

### Required Materials

Materials to Gather

Building On

Building Towards

### Lesson Timeline

 Warm-up 10 min Activity 1 10 min Activity 2 25 min Lesson Synthesis 10 min Cool-down 5 min

### Teacher Reflection Questions

In what ways did students extend and apply their understanding of multiplication and area throughout the lesson?

### Suggested Centers

• Mystery Number (1–4), Stage 6: Decimals (Supporting)

### Print Formatted Materials

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