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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.
A hexagon.
A triangle.
A four-sided figure.

## 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?
A trapezoid with sides labeled as follows: 18 meters, 8 meters, 10 meters, and 10 meters.
We can find the perimeter by adding all of the side lengths.
A trapezoid with sides labeled as follows in different colors: 18 meters in blue, 8 meters in green, 10 meters in purple and 10 meters in red.
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?
A pentagon with sides of equal length. One side is labeled 9 centimeters.
We can find the perimeter by adding all of the side lengths.
All sides of a regular pentagon are the same length.
A pentagon with sides of equal length. All sides are labeled 9 centimeters..
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
A triangle with three sides labeled as follows: 8 centimeters, 6 centimeters, and 10 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
A six-sided polygon with the sides labeled as follows: 14 centimeters, 10 centimeters, 4 centimeters, 8 centimeters, 8 centimeters and one side with question mark centimeters.

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