Grade 2/Geometry
Perimeter: Find Missing Side Lengths (373)
Find the missing side length of a polygon or square when given the perimeter and the other side lengths.
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Quick Tip
Tip: Add the known sides and subtract from the perimeter.
Teacher Resources
Teaching Notes
Introduce perimeter as the distance around a shape. Emphasize using addition for known sides and subtraction from the 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
- Adding all given numbers without considering the total perimeter.
- Confusing perimeter with area.
- Incorrectly calculating the sum of known sides.
Differentiation
SupportUse concrete manipulatives to build shapes and measure sides.
ChallengeSolve multi-step word problems involving missing side lengths.
Discussion Questions
- What is perimeter, and why is it important?
- How do you use addition and subtraction to find a missing side?
- Can two shapes have the same perimeter but different side lengths?
- When might you need to find a missing side in real life?
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: Perimeter
Estimated Time
15 minutes
Skills Practiced
find missing side perimeteradd subtract within 100understand perimeter
Prerequisites
- Addition and subtraction within 100
- Basic polygon recognition
- Perimeter concept
Next Steps
- Solving perimeter word problems
- Calculating area of rectangles
- Calculate Perimeter of Polygons
- Perimeter Word Problems
- Area of Rectangles