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3rd grade

Course: 3rd grade > Unit 11

Lesson 1: Perimeter
Math
3rd grade
Perimeter
Perimeter
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Perimeter review

CCSS.Math:
3.MD.D.8
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 start color #11accd, start text, b, l, u, e, end text, end color #11accd.
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.
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
Want to learn more about calculating perimeter? Check out this video.

Practice set 1: Calculate perimeter

Problem 1A
  • Current
What is the perimeter of the triangle?
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4
  • a mixed number, like 1, space, 3, slash, 4
  • an exact decimal, like 0, point, 75
  • a multiple of pi, like 12, space, start text, p, i, end text or 2, slash, 3, space, start text, p, i, end text
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?
  • Your answer should be
  • an integer, like 6
  • an exact decimal, like 0, point, 75
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4
  • a mixed number, like 1, space, 3, slash, 4
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

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