Lesson 7
Ways to Find Unknown Length (Part 1)
Lesson Purpose
The purpose of this lesson is for students to use the known attributes of twodimensional figures (such as side lengths and symmetry) to reason about the perimeter of shapes.
Lesson Narrative
In previous lessons, students examined the attributes of twodimensional figures. They identified, sorted, and drew figures based on side length, angle size, presence of parallel or perpendicular sides, and symmetry. In this lesson, students use their understanding of these attributes to find the perimeter of different shapes. In the first activity, students find the perimeter of shapes when all side lengths are given and connect the perimeter of different shapes to equations. In the second activity, students are asked to find the perimeter of shapes when some side lengths are not given. Students use what they have learned about analyzing the attributes of shapes to determine if the perimeters can be found or if they need more information.
 Representation
 MLR8
Learning Goals
Teacher Facing
 Find the perimeter of twodimensional shapes using their properties.
Student Facing
 Let’s find the perimeter of different shapes.
Required Materials
Materials to Gather
Required Preparation
CCSS Standards
Lesson Timeline
Warmup  10 min 
Activity 1  20 min 
Activity 2  15 min 
Activity 3  10 min 
Lesson Synthesis  10 min 
Cooldown  5 min 
Teacher Reflection Questions
Earlier in the unit, students looked closely at the attributes of twodimensional figures. In what ways did you see students applying their understanding to find perimeter? How can you continue to foster connections between different geometric ideas in upcoming lessons?
Suggested Centers
 Which One? (K–5), Stage 5: Grade 4 Shapes (Addressing)
 Can You Draw It? (1–5), Stage 5: Grade 4 Shapes (Addressing)
 Compare (1–5), Stage 5: Fractions (Supporting)
 Compare (1–5), Stage 7: Multidigit Operations (Supporting)
Print Formatted Materials
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Additional Resources
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