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Geometry (all content)

Course: Geometry (all content) > Unit 7

Lesson 3: Perimeter
Math
Geometry (all content)
Area and perimeter
Perimeter
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Perimeter review

Google Classroom
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 blue.
A hexagon.
A triangle.
A four-sided figure.
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?
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.
Perimeter=18+8+10+10
Perimeter=46 m

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..
Perimeter=9+9+9+9+9
Perimeter=45 cm
Want to learn more about calculating perimeter? Check out this video.

Practice set 1: Calculate perimeter

Problem 1A
What is the perimeter of the triangle?
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3/5
  • a simplified improper fraction, like 7/4
  • a mixed number, like 1 3/4
  • an exact decimal, like 0.75
  • a multiple of pi, like 12 pi or 2/3 pi
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
The perimeter of the figure is 50 cm.
What is the length of the missing side?
  • Your answer should be
  • an integer, like 6
  • an exact decimal, like 0.75
  • a simplified proper fraction, like 3/5
  • a simplified improper fraction, like 7/4
  • a mixed number, like 1 3/4
cm
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

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