Submarine maths quest: perimeter
A story-led junior maths adventure using depths, pressure and hidden coordinates to measure fences, walls and safe zones around places.
Quick answer
Perimeter is the total distance around the edge of a shape. You can find it by adding up all the sides of a shape.
Learning outcome
By the end of this page, you will be able to measure the perimeter of any shape by adding up all its sides.
- You can identify the sides of a shape
- You can add up the sides to find the total distance around a shape
- You can measure shapes in real life, like your garden or bedroom
- You can use perimeter to help plan safe zones or fencing
Why this matters
Perimeter helps us know how much fencing we need for a garden, how far we run around a playground, or how much border we need for a picture frame. In the story of the submarine, knowing the perimeter helps the crew plan safe zones around their underwater base. It's useful in real life for building, gardening, and even playing games!
How it works
Perimeter means "the distance around the edge of a shape". To find it:
- Look at all the sides of the shape
- Measure each side
- Add all the sides together
- You have the perimeter!
For example, if a rectangle has sides of 4m, 4m, 3m, and 3m, the perimeter is 4 + 4 + 3 + 3 = 14m.
Examples you can see
Imagine you're helping the submarine crew build a safe zone around their base. They need to know how far the fence should go around the area.
Example 1: Square base
The submarine's base is a square with each side measuring 5 metres.
| Side | Length |
|---|---|
| Side 1 | 5m |
| Side 2 | 5m |
| Side 3 | 5m |
| Side 4 | 5m |
Total perimeter = 5 + 5 + 5 + 5 = 20m
Example 2: Rectangular base
The submarine's control room is a rectangle with sides of 6m and 4m.
| Side | Length |
|---|---|
| Side 1 | 6m |
| Side 2 | 4m |
| Side 3 | 6m |
| Side 4 | 4m |
Total perimeter = 6 + 4 + 6 + 4 = 20m
Example 3: Triangular base
The submarine's emergency shelter is a triangle with sides of 3m, 4m, and 5m.
| Side | Length |
|---|---|
| Side 1 | 3m |
| Side 2 | 4m |
| Side 3 | 5m |
Total perimeter = 3 + 4 + 5 = 12m
Try it as a mini adventure
Join the submarine crew on their mission to find the perimeter of their underwater base!
Adventure: The Perimeter Quest
As a young explorer, you are helping the submarine crew plan their safe zones. They have three areas to measure:
Area 1: The Main Lab
It's a square with each side measuring 7m.
What is the perimeter?
7 + 7 + 7 + 7 = 28m
Area 2: The Storage Room
It's a rectangle with sides of 5m and 3m.
What is the perimeter?
5 + 3 + 5 + 3 = 16m
Area 3: The Emergency Bay
It's a triangle with sides of 4m, 4m, and 6m.
What is the perimeter?
4 + 4 + 6 = 14m
Great job! You've helped the submarine crew plan their safe zones.
Common mistakes
- Mistake: Only adding two sides of a rectangle instead of all four sides.
Why it happens: Children might think a rectangle only needs two measurements.
Fix: Always count all sides and make sure you're adding four sides for a rectangle.
- Mistake: Forgetting to measure all sides.
Why it happens: Children might get distracted or confused by shapes.
Fix: Use your finger to trace around the shape and count each side as you go.
- Mistake: Adding the same side twice.
Why it happens: Children might accidentally count the same side twice when adding.
Fix: Write each measurement down before adding them up to avoid confusion.
Parent and carer guide
Help your child practice finding perimeter by:
- Measuring the sides of a room or garden with a ruler or tape measure
- Using everyday objects like books, boxes, or toys to make shapes
- Playing a game where you ask them to find the perimeter of different objects
- Encouraging them to draw shapes and calculate the perimeter
- Connecting the concept to real-life situations like fencing a garden or planning a playground
Remember to celebrate their successes and gently correct mistakes. It's okay if they make errors – that's how they learn!
Practice questions
- What is the perimeter of a square with sides of 6m?
- What is the perimeter of a rectangle with sides of 8m and 5m?
- What is the perimeter of a triangle with sides of 3m, 4m, and 5m?
- What is the perimeter of a square with sides of 10m?
- What is the perimeter of a rectangle with sides of 7m and 3m?
Answers:
- 6 + 6 + 6 + 6 = 24m
- 8 + 5 + 8 + 5 = 26m
- 3 + 4 + 5 = 12m
- 10 + 10 + 10 + 10 = 40m
- 7 + 3 + 7 + 3 = 20m
FAQ
What is perimeter?
Perimeter is the total distance around the edge of a shape. You find it by adding up all the sides.
How do I measure perimeter?
Measure each side of the shape, then add all the measurements together. The sum is the perimeter.
Can I find perimeter for any shape?
Yes! You can find the perimeter of any shape as long as you can measure all its sides.
Why is perimeter useful?
Perimeter helps us know how much fencing we need, how far we run, or how much material we need for borders.
What's the difference between area and perimeter?
Perimeter is the distance around the outside of a shape. Area is the space inside the shape.