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Maths Adventures

Spy maths quest: perimeter

A story-led junior maths adventure using codes, gadgets and secret missions to measure fences, walls and safe zones around places.

Quick answer

Perimeter is the total distance around the edge of a shape. You measure it by adding up all the sides.

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. Success signs:
  • You can identify all the sides of a shape
  • You can add up the sides correctly
  • You can measure and calculate the perimeter of rectangles and squares
  • You can use real-world examples to find perimeters

Why this matters

Perimeter is like a secret code that helps spies and detectives know how much fencing they need for a safe zone, how far they need to run around a park, or how much border they need for a secret map. In real life, it helps you work out how much material you need for a garden fence, how far you've walked around a block, or how much ribbon you need to trim a picture frame.

How it works

To find the perimeter of a shape, you need to:
  1. Look at all the sides of the shape
  2. Measure each side (or know the length of each side)
  3. Add all the sides together

Examples you can see

Let's imagine you are a secret agent and need to measure the perimeter of your spy base. Your base is a rectangle that is 5 metres wide and 3 metres long. Step 1: Identify the sides.
  • Two sides are 5 metres long (the width)
  • Two sides are 3 metres long (the length)
Step 2: Add all sides together.
  • 5 + 3 + 5 + 3 = 16 metres
Step 3: The perimeter is 16 metres. Here's another example with a square spy safe room that is 4 metres on each side.
  • Four sides are 4 metres each
  • 4 + 4 + 4 + 4 = 16 metres

Try it as a mini adventure

Secret Mission: The Spy Base Perimeter Challenge You are a secret agent who has just received a new mission. Your spy base is shaped like a rectangle. You need to measure how much fencing you need to surround your base. Task: Measure the perimeter of your spy base. Materials needed: Measuring tape or ruler, paper, pencil Step-by-step mission: 1st time: Draw a rectangle on paper and label it 6 metres wide and 4 metres long. 2nd time: Measure each side and write the measurements on your drawing. 3rd time: Add up all the sides: 6 + 4 + 6 + 4 = ? 4th time: You need 20 metres of fencing to surround your base. 5th time: Try again with a different shape like a pentagon (5 sides) that is 3 metres each. 6th time: Add up all five sides: 3 + 3 + 3 + 3 + 3 = ? 7th time: The perimeter is 15 metres. 8th time: You've completed your secret mission!

Common mistakes

  • Mistake: Forgetting to measure all sides of a shape
    Why it happens: The spy is in a hurry and gets distracted by the secret mission
    Fix: Make a list of all sides before adding them up, or use a finger to trace each side while counting
  • Mistake: Adding only two sides instead of all sides
    Why it happens: The agent thinks it's enough to measure just the length and width
    Fix: Remember that perimeter means all around the outside, so measure every side
  • Mistake: Confusing perimeter with area
    Why it happens: Both involve shapes and measurements, so they can be mixed up
    Fix: Perimeter is the distance around the outside, area is the space inside the shape

Parent and carer guide

You can help your child practice perimeter with these simple activities:
  • Measure the perimeter of your living room or bedroom using a tape measure or ruler
  • Draw shapes on paper and have your child add up the sides
  • Play a game where you race to find the perimeter of different objects around the house
  • Use real objects like books, boxes, or toys to practice measuring and adding sides
  • Encourage your child to think about when they might use perimeter in real life, like when they're helping to build something or plan a garden
What to say: "Let's measure how far around this table is by adding up all the sides." What not to worry about: Your child might mix up the units or make small addition mistakes. These are normal learning steps. Focus on the process of measuring and adding rather than getting the exact answer right away.

Practice questions

  1. What is the perimeter of a rectangle that is 7 metres wide and 5 metres long?
  2. Calculate the perimeter of a square with sides of 6 metres
  3. A triangle has sides of 4 metres, 5 metres, and 3 metres. What is its perimeter?
  4. Find the perimeter of a rectangle that is 10 metres wide and 8 metres long
  5. What is the perimeter of a square that is 9 metres on each side?
Answers:
  1. 7 + 5 + 7 + 5 = 24 metres
  2. 6 + 6 + 6 + 6 = 24 metres
  3. 4 + 5 + 3 = 12 metres
  4. 10 + 8 + 10 + 8 = 36 metres
  5. 9 + 9 + 9 + 9 = 36 metres

FAQ

What is perimeter?

Perimeter is the total distance around the outside edge of a shape.

How do I find the perimeter of a square?

Since all sides of a square are equal, you can multiply one side by 4 to find the perimeter.

Can I use any unit to measure perimeter?

Yes, you can use any unit like centimetres, metres, inches, or feet, as long as you use the same unit for all measurements.

Why is perimeter important in real life?

Perimeter helps you know how much fencing you need, how far you've walked, how much material you need for borders, and much more.

What if a shape has more than 4 sides?

You still add up all the sides. For example, a pentagon (5 sides) has a perimeter of side 1 + side 2 + side 3 + side 4 + side 5.