Calculate the Perimeter: Rectangle with Dimensions 9 by 5 Units

Q: What's the difference between perimeter and area?

Perimeter is the distance around the outside of a shape (add all sides). Area is the space inside the shape (multiply length × width for rectangles). Don't mix them up!

Q: Do I really need to add all four sides separately?

You can use the shortcut formula P = 2(length + width)! This works because opposite sides of a rectangle are equal, so you're really doing 2 × length + 2 × width.

Q: How do I know which sides are equal in a rectangle?

In a rectangle, opposite sides are always equal. So if one side is 9 units, the side across from it is also 9 units. Same with the other pair!

Rectangle Perimeter with Given Dimensions

Look at the following rectangle:

Find its perimeter.

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Find the perimeter of the rectangle

00:03 The perimeter of the rectangle equals the sum of its sides

00:16 Opposite sides in a rectangle are equal

00:20 Let's substitute appropriate values according to the given data and solve for the perimeter

00:31 Let's solve for each 2 factors separately and then sum them

00:36 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

Look at the following rectangle:

Find its perimeter.

Step-by-step solution

Since in a rectangle all pairs of opposite sides are equal:

$AD=BC=5$

$AB=CD=9$

Now we calculate the perimeter of the rectangle by adding the sides:

$5+5+9+9=10+18=28$

Final Answer

Key Points to Remember

Essential concepts to master this topic

Formula: Perimeter of rectangle equals sum of all four sides
Technique: Add opposite sides: 9 + 9 + 5 + 5 = 28
Check: Use formula P = 2(length + width) = 2(9 + 5) = 28 ✓

Common Mistakes

Avoid these frequent errors

Multiplying length times width instead of adding all sides
Don't calculate 9 × 5 = 45 for perimeter! This gives you the area, not the distance around the rectangle. Always add all four sides: length + length + width + width.

Practice Quiz

Test your knowledge with interactive questions

Calculate the perimeter of the rectangle below.

FAQ

Everything you need to know about this question

What's the difference between perimeter and area?

Perimeter is the distance around the outside of a shape (add all sides). Area is the space inside the shape (multiply length × width for rectangles). Don't mix them up!

Do I really need to add all four sides separately?

You can use the shortcut formula P = 2(length + width)! This works because opposite sides of a rectangle are equal, so you're really doing 2 × length + 2 × width.

What if the rectangle is turned sideways in the diagram?

The orientation doesn't matter! Just identify which measurement is the length (longer side) and which is the width (shorter side), then apply the perimeter formula.

How do I know which sides are equal in a rectangle?

In a rectangle, opposite sides are always equal. So if one side is 9 units, the side across from it is also 9 units. Same with the other pair!

Can I check my answer a different way?

Yes! Try walking around the rectangle: start at one corner and add up the distances. You should get the same answer as the formula $P = 2(l + w)$ .

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