Year 4 - Maths
Know that unknown side lengths can be calculated from the perimeter and known side lengths
Perimeter
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This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
Unit Summary
In this unit pupil will learn perimeter as the distance around the edge of a 2D shape. They will learn perimeter is measured in units of length found by counting units and by calculating by adding the side lengths of a 2D shape.
Lesson Summary
You will learn to calculate unknown side lengths of rectangles from the perimeter and known side lengths.
Key Notes
- Subtraction and halving can be used to calculate the missing side length of a rectangle.
- If you know the perimeter and one of the side lengths you can subtract the known sides and halve the difference.
- Mental and written methods can be used to calculate the perimeter of a 2D shape.
Vocabulary To Learn
- Perimeter: The distance around a two-dimensional shape.
Common Mistakes To Avoid
- Pupils may see a rectangle with the perimeter given and only one of the side lengths and think that there is insufficient information as there are three missing side lengths.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
Subtraction and halving can be used to calculate the missing side length of a rectangle. If you know the perimeter and one of the side lengths you can subtract the known sides and halve the difference.
2. Use this key word in a maths sentence and explain it clearly. 'Perimeter'
The distance around a two-dimensional shape. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Pupils may see a rectangle with the perimeter given and only one of the side lengths and think that there is insufficient information as there are three missing side lengths. Correction: Remind pupils that because it is a rectangle, the side length opposite the given side length is in fact known. A counter can be added on and then removed again to show that they actually know two of the missing side lengths, not just one.
More Lessons In This Unit
- Calculate the side length of a regular polygon by division where the perimeter is known Study Guide
- Know that a regular polygon has sides that are the same length and angles that are the same size Study Guide
- Know that perimeter can be calculated by adding together the side lengths of a 2D shape Study Guide
- Know that perimeter is measured in units of length and can be found by counting or measuring units Study Guide
- Know that the perimeter is the distance around a 2D shape Study Guide
- Know that the perimeter of a rectangle can be calculated by addition and multiplication Study Guide
- Solve problems involving the perimeter and side lengths of polygons Study Guide
- Understand that different shapes can have the same perimeter Study Guide
- Understand that the perimeter of a regular polygon can be calculated by multiplication Study Guide
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