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### Course: 3rd grade > Unit 11

Lesson 1: Perimeter- Perimeter: introduction
- Perimeter of a shape
- Find perimeter by counting unit squares
- Find perimeter by counting units
- Finding perimeter when a side length is missing
- Find perimeter when given side lengths
- Finding missing side length when given perimeter
- Perimeter review

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# Perimeter review

Review the basics of perimeter and try some practice problems.

## What is perimeter?

Perimeter is the distance around the outside of a two-dimensional shape.

The perimeter of the shapes below is shown in ${\text{blue}}$ .

*Want to learn more about the concept of perimeter? Check out this video.*

## How do we calculate the perimeter of a shape?

To find the perimeter of a shape, we add all of the shape's side lengths.

### Example 1:

**What is the perimeter of the trapezoid?**

We can find the perimeter by adding all of the side lengths.

### Example 2:

**What is the perimeter of the regular pentagon?**

We can find the perimeter by adding all of the side lengths.

All sides of a

*regular*pentagon are the same length.*Want to learn more about calculating perimeter? Check out this video.*

## Practice set 1: Calculate perimeter

*Want to try more problems like this? Check out these exercises:*

Find perimeter when given side lengths

Find perimeter by counting unit squares

## Practice set 2: Challenge items

*Want to try more problems like this? Check out these exercises:*

Find a missing side length when given perimeter

Perimeter word problems

## Want to join the conversation?

- If two or more sides of a shape is unknown, what can you do to figure that out?(65 votes)
- If you want to figure it you have to see the othr stuff first then you would figure it out but if not i don't know it worked for me(7 votes)

- How will I use this in real life?(27 votes)
- well... if you r going to build a house u will need to know the perimeter.(6 votes)

- its a bit challenging though. you really need analyzing skills for it ahaha.(13 votes)
- can you calculate this problem please. A piece of wire 80cm long is bent to form a rectangle. Find the dimensions of the rectangle so that its area us as large as possible.(7 votes)
- A square will give most area. Square with four sides of 20cm each. Therefore to find area we multiply length * width: 20 * 20 = 400 cm²(11 votes)

- how can you see perimeter in 3D polygons(14 votes)
- I love this so fun it is so fantastic(11 votes)
- Why do you put this here why why!(0 votes)

- what is 100x10,000000?(3 votes)
- A certain number.(15 votes)

- If two or more sides of a shape is unknown, what can you do to figure that out?(4 votes)
- Well, it depends on the shape, really...(4 votes)

- Yeah, I agree, Mr. Taylor—I got confused, the angle change puzzled me, but I realized my mistake and corrected it.(9 votes)