Grade 3/Geometry
Area of L-Shaped Figures (718)
Find the area of L-shaped figures by decomposing them into two rectangles and adding the partial areas.
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Teacher Resources
Standards
CCSS.MATH.CONTENT.3.G.A.1Teaching Notes
Teach students to visualize splitting L-shapes vertically or horizontally. Emphasize labeling partial areas and applying correct units.
Vocabulary
L-shape: A shape like the letter L.
Decompose: Break a shape into smaller parts.
Common Mistakes
- Multiplying the wrong pairs of side lengths.
- Forgetting to add both rectangle areas.
- Dropping the square-unit label in the final answer.
- Mixing up rectangle dimensions
- Incorrectly decomposing figures
- Forgetting to add partial areas
- Incorrectly labeling units
Differentiation
SupportUse grid paper to draw shapes and count individual squares.
ChallengeChallenge students to solve by subtracting an 'empty' rectangle.
Discussion Questions
- How many ways can you decompose an L-shaped figure?
- Why is it important to label your partial rectangles?
- When might you need to find the area of an L-shape in real life?
- How is finding area different from finding perimeter?
Extension Activities
- Find area of U-shapes.
- Find area of T-shapes.
- Calculate perimeter of L-shapes.
Parent Tip
Use blocks to build L-shapes and find their area.
Learning Path
Skill Cluster
Measurement and Geometry
Estimated Time
18 minutes
Skills Practiced
Splitting rectilinear figures into rectanglesComputing area with multiplicationAdding partial areas with unitsInterpreting labeled diagrams
Prerequisites
- Area of rectangles
- Decomposing composite shapes
- Area of Rectangles
- Multiplication Facts
- Addition of Whole Numbers
Next Steps
- Area of More Complex Composite Shapes
- Area of Irregular Polygons on Grids
- Area of Rectangles
- Perimeter of Rectilinear Shapes
- Area & Perimeter Word Problems