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Why is this concept useful?: Perimeter is used often in daily life for measuring enclosures, tracking distance on a run, and anytime you may need to know the distance around a polygonal shape.
Where does this concept fit into the curriculum?: Grade 3

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By Puja Varude

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How can we use the concept:

Perimeter in its most basic form can be found by adding all the sides of a polygon together. However, there are a couple of formula used regularly, have a look at them below:

Perimeter of a Rectangle:

There are several ways to write the perimeter of a rectangle. The most common are:

P = (2 \times L) + (2 \times W)

P = 2 \cdot (L + W)

Remember: L stands for the length, and W stands for the width of a rectangle

Perimeter of a Square:

A square is a special rectangle where all sides are equal, so in this one instance, we do not need a length or a width, any side can help us find the perimeter.

P = 4 \times S

Where S stands for the length of the side of the square

Sample Math Problems

Question

Perimeter of a rectangle where

L=7

and

W = 13

Solution

Use

P = 2 \cdot (L + W)

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Practice Math Problems

1.) Perimeter of a rectangle with l=3 and w=8

2.) Find the missing side of this shape with P = 42

3.) The perimeter of a regular 10 sided polygon is 80cm. What is the sum of 3 sides of the polygon?

4.) Which of the following can be used to find the perimeter of a fence for a dog pen that is 9 feet long and 6 feet wide? (More than one solution may be correct.

P=2(9+6)
P=9 x 6
P=2+9 x 6
P=2 x 9+2 x 6

Replace length with 7 and width with 13

P=2\times(7+13)

Solve

P = 2 \times 20

P=40

Question

Find the missing side when P = 24

Solution

P=24

P=3+7+5+4+?+3

P=22+?

24=22+ ?

24=22+ 2

So the missing side length is 2.

Question

The perimeter of a regular 7 sided polygon is 42 cm. What is the sum of 4 sides of the polygon?

Solution

The perimeter of a regular 7 sided polygon is 42 cm. What is the sum of 4 sides of the polygon?

A regular polygon has all the sides the same length.This means that we can treat it like a square and multiply one side length times the number of sides to get the perimeter. Thus, 7 x side = 42cm; since 76 = 42, then side = 6cm. We can now use the side length to find the sum of 4 sides. Finding the sum of the sides would be 6cm + 6cm + 6cm + 6cm, or 46cm, which is 24 cm.

Question

Which of the following options is the correct calculation to find the perimeter of a fence for a yard that is 30 feet long and 45 feet wide?

Option A:

P = 2(45+30)

Option B:

P=45\times30

Option C:

P= 2 + 45 \times 30

Option D:

P=2\times45 +2\times30

Solution

Perimeter is 30 ft. + 45 ft. + 30 ft. + 45 ft. = 150 ft.

Even if we do know if the formula fits for the perimeter, we can check the solutions of each option and see if we get the same as our sum.

Option A:

P = 2(45+30) = 150 \checkmark

Option B:

P=45\times30 = 1350 \neq 150

Option C:

P= 2 + 45 \times 30 = 1352 \neq 150

Option D:

P=2\times45 +2\times30 = 150 \checkmark

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Geometry Worksheets

Perimeter of a Shape

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Math Tutoring to Boost Your Child’s Math Skills & Scores by 90% in Just 3 Months – Guaranteed!

Sample Math Problems

Download FREE Math Resources

8 Math Hacks and Tricks to Turn Your 'Okay' Math Student Into a Math Champion!

How to Make Sure Your Child is Highly Successful and Becomes a Millionaire

Practice Math Problems