Perimeter of a Rectangle

Lesson Objective

In this lesson, we will learn about the perimeter of a rectangle.

Study Tips

Tip #1

A rectangle has four right angles. The sides of a rectangle that are opposite each other have the same length.

Now, if a rectangle has the length of l and the width of w, its perimeter, P, will be the total distance around the outside of the rectangle. Hence:

P = 2(l+w)

a rectangle with the length l and width w

The math video below will give more explanation on this. Also, we will see some examples on how to use this formula.

Math Video

Video on the perimeter of a rectangle

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Video on the examples on using the formula P=2(l+w)

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Math Videos Transcript

PART 1

00:00:04.000
In this lesson, we will learn about the perimeter of a rectangle.

00:00:09.030
Consider this rectangle. This rectangle has the length of L and the width of W.

00:00:17.000
Since, the perimeter of the rectangle, P, is the total distance around the outside of the rectangle, the perimeter, will be equals to  L, add with W, add with another L, and finally, add with another W.

00:00:39.020
Let's simplify this. L add with L, gives 2L. Similarly, W add with W, gives 2W.

00:00:52.110
Notice that, these two terms have '2' as a common factor.  

00:00:58.140
Hence, by taking out '2', we have, 2(L+W).

00:01:06.070
Therefore, the perimeter, P = 2(L+W).

00:01:15.000
Let's rewrite it here.

00:01:18.100
Note that, in any calculation, when we found the value of P, it is important to include the unit.

00:01:26.140
For example, if L and W are given in centimeter, the unit for the perimeter will be in centimeter as well.

00:01:35.230
The next video will show some examples on using this formula.


PART2

00:00:04.020
After understanding the formula for the perimeter of a rectangle, let's see some examples on using the formula.

00:00:12.080
Find the perimeter of this rectangle, when its length is 4cm, and its width is 3cm.

00:00:20.010
We start with the formula for the perimeter of a rectangle, P=2(L+W).

00:00:29.060
Since the length of the rectangle is given as 4cm, we can substitute, L with 4.

00:00:37.070
Similarly, since the width is given as 3cm, we can substitute W with 3.

00:00:45.060
Let's simplify this. 4 add with 3, gives 7. 2 multiply with 7, gives 14.

00:00:57.110
Hence, we have P=14.

00:01:02.210
Now, this number doesn't mean anything, unless we include the unit for it.

00:01:09.060
Since the length, and the width, are given in centimeter, the unit for the perimeter will also be in centimeter.

00:01:17.110
Therefore, the perimeter of this rectangle is equals to 14cm.

00:01:25.050
Next example, the perimeter of this rectangle, is 24ft, and its width is 5ft. Find its length.

00:01:37.060
Again, we start with the formula for the perimeter of a rectangle, P=2(L+W).

00:01:46.030
Since the perimeter, and the width of the rectangle are given, we can find the length of the rectangle, by solving this equation for L.

00:01:56.080
Let's start. The perimeter is given as 24ft. Therefore, we can substitute P with 24.  

00:02:08.210
Similarly, since the width is given as 5ft, we can substitute W with 5.

00:02:17.150
Now, to get a step closer in finding L, we need to remove '2'.

00:02:24.110
To do so, we divide both sides of the equation with 2. This gives, 24 over 2, equals to L plus 5.

00:02:37.020
24 divided by 2, gives 12.

00:02:41.150
Now, we have, L plus 5, equals to 12.

00:02:48.030
Let's rewrite this equation so that it looks neater.

00:02:52.170
Next, to find L, we need to remove 5. To do so, we add -5 to both sides of the equation.

00:03:03.090
By doing so, we get, L equals to 12 minus 5. 12 minus by 5, gives 7.

00:03:13.170
Now, we have, L equals to 7. Note that, this number doesn't mean anything, unless we include the unit for it.

00:03:25.110
Since the width is in feet, the length will also be in feet.

00:03:31.050
Finally, the length of this rectangle is 7ft.

00:03:37.110
That is all for this lesson. Try out the practice question to further your understanding.

Practice Questions & More

Multiple Choice Questions (MCQ)

Now, let's try some MCQ questions to understand this lesson better.

You can start by going through the series of questions on the perimeter of a rectangle or pick your choice of question below.

Question 1 on finding the perimeter of a rectangle
Question 2 on finding the width of a rectangle

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