# Lesson 9

Perimeter Problems

### Lesson Purpose

The purpose of this lesson is for students to find unknown side lengths given the perimeter of a shape and solve problems involving perimeter.

### Lesson Narrative

In previous lessons, students learned how to find the perimeter of shapes given all sides lengths or some side lengths. In this lesson, students use their understanding of perimeter to find missing side lengths when given the perimeter. Then, students solve problems in situations that involve perimeter. This lesson prepares students to think carefully about the difference between perimeter and area, which will be addressed in subsequent lessons.

• Engagement
• MLR8

### Learning Goals

Teacher Facing

• Find unknown side lengths given the perimeter of a shape.
• Solve problems that involve perimeters of shapes.

### Student Facing

• Let’s solve problems about perimeter.

### Lesson Timeline

 Warm-up 10 min Activity 1 15 min Activity 2 20 min Lesson Synthesis 10 min Cool-down 5 min

### Teacher Reflection Questions

How are students working toward multiplication and division fluency while solving perimeter problems?

### Suggested Centers

• Can You Draw It? (1–5), Stage 3: Grade 3 Shapes (Addressing)