Grade 3/Geometry
Missing Side from Perimeter (374)
Find the missing side length of a polygon or square using the diagram and the given perimeter.
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Quick Tip
Tip: Add the known sides and subtract from the perimeter.
Teacher Resources
Teaching Notes
Introduce perimeter as the total distance around a shape. Guide learners to sum known sides and subtract from the given total perimeter to find the missing length.
Vocabulary
Perimeter: The total distance around the outside of a shape.
Side length: The measurement of one edge of a shape.
Common Mistakes
- Forgetting to add all known side lengths before subtracting.
- Subtracting from a known side instead of the total perimeter.
- Misidentifying which sides are known or unknown on the diagram.
Differentiation
SupportUse string or blocks to build shapes and measure sides physically.
ChallengeChallenge with shapes having more sides or multi-step problems.
Discussion Questions
- What does 'perimeter' mean in your own words?
- Why is it helpful to know the perimeter of a shape?
- How is finding a missing side length different from just finding the perimeter?
- Can two different shapes have the same perimeter?
Extension Activities
- Draw shapes with given perimeters.
- Find missing sides of irregular shapes.
- Calculate perimeter of real objects.
Parent Tip
Help your child measure the edges of objects around the house.
Learning Path
Skill Cluster
Measurement and Geometry
Estimated Time
15 minutes
Skills Practiced
find missing side perimeteradd subtract within 100understand perimeter
Prerequisites
- Understand perimeter as sum of sides
- Basic addition and subtraction
Next Steps
- Solving multi-step perimeter problems
- Perimeter with fractional side lengths
- Perimeter of Rectangles and Squares
- Finding Missing Dimensions: Area
- Perimeter of Irregular Polygons