Grade 3/Geometry
Perimeter of Composite Figures (1123)
Calculate the perimeter of L-shaped composite figures.
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Quick Tip
Add all the outer side lengths together. Hint: For L-shapes, Perimeter = 2 × (Total Width + Total Height).
Teacher Resources
Teaching Notes
This collection focuses on perimeter of composite figures. Use grid paper to help students visualize area and perimeter.
Vocabulary
Perimeter: Distance around a 2D shape.
Composite Figure: A shape made of smaller shapes.
Common Mistakes
- Confusing Area and Perimeter formulas
- Forgetting to double the sides for Perimeter
- Using wrong units (e.g., cm instead of sq cm for Area)
- Forgetting hidden side lengths.
- Adding interior partition lines.
- Confusing perimeter with area.
- Arithmetic calculation errors.
Differentiation
SupportHave students trace shapes on grid paper and count squares.
ChallengeChallenge students to find multiple rectangles with the same area but different perimeters.
Discussion Questions
- What is the difference between Area and Perimeter?
- Can two rectangles have the same perimeter but different areas?
- Why do we use 'square' units for area?
- How do we find all the outer edge lengths?
- What strategies help find unknown side lengths?
- Why is knowing perimeter useful in real life?
- How does an L-shape relate to a rectangle?
Extension Activities
- Measure the classroom floor area.
- Design a garden with a specific perimeter.
- Create art using only rectangles of specific areas.
Parent Tip
Walk the perimeter of your home and count steps for each side.
Learning Path
Skill Cluster
Geometry and Measurement
Estimated Time
20 minutes
Skills Practiced
perimeter of composite figures
Prerequisites
- 1122
- Perimeter of Rectangles
- Adding Whole Numbers
Next Steps
- Area of Composite Figures
- Perimeter of Irregular Polygons
- Perimeter of Rectangles
- Missing Side Lengths (Perimeter)