Area of a Rectangle

Lesson Objective

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

About This Lesson

In this lesson, we will:

Learn about the formula to find the area of a rectangle.
See an example on using the formula to calculate a rectangle's area.
See another example on using the formula to calculate the width of a rectangle.

The study tips and math video below will explain more.

Study Tips

Tip #1

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

Note that, the longer side of a rectangle is the length and the shorter side is the width. Also, a square is a special type of rectangle.

Now, for a rectangle with length l and width w, its area, A will be:

A = lw

a rectangle with the length l and width w

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

Math Video

Lesson Video

Math Video Transcript

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

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Consider this rectangle with the length of L, and the width of W.

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Now, we can get the area of the rectangle, by multiplying its length L with its width W.

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With this, we get the area, A equals to, L multiply W. This gives LW.

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Note that, it is very important to include the unit. Since we are multiplying L with W, the unit for the area will be in the form of square unit.

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We will see more explanations on this in the upcoming example.

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Now, let's see some examples on using this formula.

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Find the area of this rectangle when its length is 4cm, and its width is 3cm.

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To solve this, we start with the formula for the area of a rectangle, A equals to LW.

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Since the length is given as 4cm, we can substitute L with 4.

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Similarly, since the width is given as 3cm, we can substitute w with 3.

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Next, we can simplify by multiplying 4 with 3. This gives 12.

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Now, this number is meaningless unless we include the unit for it.

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Since the length and width are given in centimeter, the unit for the area will be in square centimeter.

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Hence, the area of this rectangle is 12 square centimeter.

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Next example, given that the area of this rectangle is 20 square feet, and its length is 5ft. Find its width.

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Again, we start with the formula for the area of a rectangle, A equals to LW.

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Since the value of the area and the length is given, we can find the width, by solving this equation for w.

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Here’s how. Since the area is given as 20 square feet, we can substitute A with 20.

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Similarly, since the length is given as 5ft, we can substitute l with 5.

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Now we have, 5w equals to 20.

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Let's rewrite this equation so that it will look neater.

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To find W, we need to remove 5. To do so, we divide both sides of the equation with 5.

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After doing so, we have, W equals to 20 over 5.

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20 divide by 5 gives 4.  

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Now, this number is meaningless unless we include the unit for it.

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Since the length is given in feet, the width of the rectangle will also be in feet.

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Therefore, the width of this rectangle is 4 ft.

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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 area of a rectangle or pick your choice of question below.

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

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