3) Which triangle has a perimeter of $ 41 $ units?

4) Which are the sides of a triangle with a perimeter of $ 50{~cm}? $

$ 15{~cm}, \, 20{~cm}, \, 15{~cm} $

$ 12{~cm}, \, 13 {~cm}, \, 14{~cm} $

$ 20{~cm}, \, 5{~cm}, \, 20{~cm}, \, 5{~cm} $

Perimeter of a Triangle - Math Steps, Examples & Questions

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Math resources Geometry Perimeter

Perimeter of a triangle

Here you will learn how to find the perimeter of a triangle, including what the perimeter is, how to calculate it and how to solve perimeter word problems.

Students will first learn how to find perimeter as part of measurement and data in 3rd grade.

What is the perimeter of a triangle?

The perimeter of a triangle is the total distance around the outside of the triangle.

For example,

Perimeter is measured in units, like inches.

Measuring the perimeter is like starting at one vertex of a triangle and measuring the total distance around the triangle.

The perimeter can also be calculated by adding the length of each side.

$katex is not defined$ so the perimeter is $katex is not defined$ inches.

What is the perimeter of a triangle?

Common Core State Standards

How does this relate to 3rd grade math?

Grade 3 – Measurement and data (3.MD.D.8)
Solve real world and mathematical problems involving perimeters of polygons, including finding the perimeter given the side lengths, finding an unknown side length, and exhibiting rectangles with the same perimeter and different areas or with the same area and different perimeters.

How to find the perimeter of a triangle

In order to calculate the perimeter of a triangle:

Add all the side lengths.
Write the final answer with the correct units.

[FREE] Perimeter Check for Understanding Quiz (Grade 3 to 4)

Use this quiz to check your grade 3 to 4 students’ understanding of perimeter. 10+ questions with answers covering a range of 3rd and 4th grade perimeter topics to identify areas of strength and support!

DOWNLOAD FREE

[FREE] Perimeter Check for Understanding Quiz (Grade 3 to 4)

DOWNLOAD FREE

How to find perimeter examples

Example 1: perimeter of an isosceles triangle

What is the perimeter of the triangle?

Add all the side lengths.

To find the perimeter (the total distance around the triangle), add all the side lengths:

$katex is not defined$

2Write the final answer with the correct units.

The side lengths are measured in feet, so the total perimeter is in feet.

The perimeter of the triangle is $katex is not defined$ feet.

Example 2: perimeter of a right triangle

What is the perimeter of the triangle?

Add all the side lengths.

Show step

To find the perimeter (the total distance around the triangle), add all the side lengths:

$katex is not defined$

Write the final answer with the correct units.

Show step

The side lengths are measured in millimeters, so the total perimeter is in millimeters.

The perimeter of the triangle is $katex is not defined$ millimeters.

Example 3: perimeter of a scalene triangle

What is the perimeter of the triangle?

Add all the side lengths.

Show step

To find the perimeter (the total distance around the triangle), add all the side lengths:

$katex is not defined$

Write the final answer with the correct units.

Show step

The side lengths are measured in centimeters, so the total perimeter is in centimeters.

The perimeter of the triangle is $katex is not defined$ centimeters.

Example 4: perimeter of equilateral triangle

What is the perimeter of the triangle?

Add all the side lengths.

Show step

To find the perimeter (the total distance around the triangle), add all the equal side lengths:

$katex is not defined$

For the perimeter of an equilateral triangle, since the sides of the triangle are the same (congruent), you can also multiply one side length by $katex is not defined$

$katex is not defined$

Write the final answer with the correct units.

Show step

The side lengths are measured in meters, so the total perimeter is in meters.

The perimeter of the triangle is $katex is not defined$ meters.

Example 5: triangle perimeter word problem

A triangular street sign has side lengths of $katex is not defined$ inches, $katex is not defined$ inches and $katex is not defined$ inches. What is the perimeter of the sign?

Add all the side lengths.

Show step

To find the perimeter (the total distance around the triangle), add all the side lengths:

$katex is not defined$

Write the final answer with the correct units.

Show step

The side lengths are measured in inches, so the total perimeter is in inches.

The perimeter of the sign is $katex is not defined$ inches.

Example 6: right scalene triangle

The perimeter of the triangle is $katex is not defined$ What is the missing side length?

Add all the side lengths.

Show step

To find the perimeter (the total distance around the triangle), add all the side lengths:

$katex is not defined$

The two sides together are $katex is not defined$ The third side is missing.

To find the missing side, think about what number added to $katex is not defined$ is $katex is not defined$

Since $katex is not defined$ the missing side length is $katex is not defined$

Write the final answer with the correct units.

Show step

The side lengths are measured in centimeters and the total perimeter is in centimeters.

The missing side length of the triangle is $katex is not defined$ centimeters.

Teaching tips for the perimeter of a triangle

Choose worksheets that have a variety of question types – varying the types of triangles – equilateral, isosceles and scalene (therefore varying the lengths of the sides), solving for the perimeter or a missing side length, word problems with or without visuals.

Give students opportunities to measure and solve problems for the perimeter of triangles in the real world.

Easy mistakes to make

Thinking the order of adding the sides matters
It doesn’t matter the order in which the sides of the triangle are added, because of the commutative property of addition. As long as all sides are added only once, they can be added in any order.

Confusing the formulas or solving strategies for perimeter with area
It is easy to confuse these two concepts, especially when first learning them. Remember that perimeter is the measurement of the length around a triangle (one-dimensional), and area is the measurement of the space within a triangle (two-dimensional).

Adding uncommon units
Side lengths need to be the same units before they can be added. If the sides are shown with different units, convert them to a common unit and then add.

Practice perimeter of a triangle questions

katex is not defined

katex is not defined

katex is not defined

katex is not defined

The perimeter (the total distance around the triangle) is the sum of the lengths of the three sides:

$katex is not defined$

The sides are measured in feet, so the perimeter is also in feet.

The perimeter is $katex is not defined$ feet.

katex is not defined

katex is not defined

katex is not defined

katex is not defined

The perimeter (the total distance around the triangle) is the sum of the lengths of the three sides:

$katex is not defined$

The sides are measured in centimeters, so the perimeter is also in centimeters.

The perimeter of triangle $katex is not defined$ is $katex is not defined$

Perimeter of a Triangle image 10 US

Perimeter of a Triangle image 11 US

Perimeter of a Triangle image 12 US

Perimeter of a Triangle image 13 US

Since the perimeter of the triangle is $katex is not defined$ units, the length of its sides should add up to $katex is not defined$

Perimeter of a Triangle image 14 US

$katex is not defined$

This triangle has a perimeter of $katex is not defined$ units.

three sides of $katex is not defined$

katex is not defined

katex is not defined

katex is not defined

A triangle has $katex is not defined$ sides. The perimeter of a triangle is the sum of the $katex is not defined$ side lengths:

$katex is not defined$

The sides of a triangle $katex is not defined$ and $katex is not defined$ have a perimeter of $katex is not defined$

$katex is not defined$ inches

The perimeter (the total distance around the triangle) is the sum of the sides:

$katex is not defined$

The two sides together are $katex is not defined$ The third side is missing.

To find the missing side, think about what number added to $katex is not defined$ is $katex is not defined$

Since $katex is not defined$ the missing side length is $katex is not defined$ inches.

$katex is not defined$ meters

Each side of an equilateral triangle is the same length, so all sides of the large garden are $katex is not defined$ meters and all sides of the smaller garden are $katex is not defined$ meters.

Large Garden: Small Garden:

Perimeter of a Triangle image 16 US

Perimeter: Perimeter:

$katex is not defined$ meters $katex is not defined$ meters

To find the difference between the perimeter of the large and small garden, subtract:

$katex is not defined$

The difference in perimeter is $katex is not defined$ meters.

Perimeter of a triangle FAQs

How do you calculate the perimeter of different types of triangles?

Since all triangles have $katex is not defined$ sides, just add the length of all three sides to find the perimeter. There are additional ways to solve for different types of triangles, like equilateral and isosceles triangles.

For equilateral triangles, multiply the length of one side by $katex is not defined$ For isosceles triangles, multiply one of the equal sides by $katex is not defined$ and then add the third side.

How do you calculate the area of a triangle?

The area of a triangle can be calculated with the formula: $katex is not defined$

Can the given sides of a triangle be fractions or decimals?

Yes, triangles can have measurements that include fractions or decimals. The perimeter is found the same way – by adding all the sides.

What is the pythagorean theorem?

It is a theorem that relates to right-angled triangles and the relationship between the two sides that form a $katex is not defined$ -degree angle and the long side, called the hypotenuse. This is a topic covered in middle school.

The next lessons are

Symmetry
Angles in polygons
Congruence and similarity
Prism shape

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