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Lesson 1: Perimeter

# 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 start color #11accd, start text, b, l, u, e, end text, end color #11accd.

## 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.
start text, P, e, r, i, m, e, t, e, r, end text, equals, start color #11accd, 18, end color #11accd, plus, start color #1fab54, 8, end color #1fab54, plus, start color #7854ab, 10, end color #7854ab, plus, start color #ca337c, 10, end color #ca337c
start text, P, e, r, i, m, e, t, e, r, end text, equals, 46, start text, space, m, end text

### 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.
start text, P, e, r, i, m, e, t, e, r, end text, equals, start color #1fab54, 9, end color #1fab54, plus, start color #1fab54, 9, end color #1fab54, plus, start color #1fab54, 9, end color #1fab54, plus, start color #1fab54, 9, end color #1fab54, plus, start color #1fab54, 9, end color #1fab54
start text, P, e, r, i, m, e, t, e, r, end text, equals, 45, start text, space, c, m, end text

## Practice set 1: Calculate perimeter

Problem 1A
• Current
What is the perimeter of the triangle?
centimeters

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

Problem 2A
• Current
The perimeter of the figure is 50, start text, space, c, m, end text.
What is the length of the missing side?
start text, c, m, end text

Want to try more problems like this? Check out these exercises:
Find a missing side length when given perimeter
Perimeter word problems