Calculate Rectangle Perimeter: 18 × 2 Units Problem

Rectangle Perimeter with Given Dimensions

Calculate the perimeter of the rectangle below.

181818222

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Calculate the perimeter of the rectangle
00:03 Apply the formula for calculating the rectangle perimeter - 2 x the sum of the sides
00:07 Insert the relevant values into the formula according to the given data and proceed to solve to find the area
00:10 Expand the brackets - multiply each factor
00:15 Solve each multiplication separately and then add together
00:20 This is the solution

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Calculate the perimeter of the rectangle below.

181818222

2

Step-by-step solution

To solve this problem, we'll start by identifying the given dimensions of the rectangle: the length l=18 l = 18 and the width w=2 w = 2 .

Next, we apply the perimeter formula for a rectangle, which is given by:

P=2(l+w) P = 2(l + w)

Substitute the given values for the length and width into the formula:

P=2(18+2) P = 2(18 + 2)

Calculating further, we find:

P=2×20=40 P = 2 \times 20 = 40

Thus, the perimeter of the rectangle is 40 40 . Among the provided answer choices, this corresponds to choice 1.

3

Final Answer

40

Key Points to Remember

Essential concepts to master this topic
  • Formula: Perimeter of rectangle equals 2(length + width)
  • Technique: Substitute values: P = 2(18 + 2) = 2(20) = 40
  • Check: Count all four sides: 18 + 2 + 18 + 2 = 40 ✓

Common Mistakes

Avoid these frequent errors
  • Adding length and width without multiplying by 2
    Don't just calculate 18 + 2 = 20! This only gives you half the perimeter because a rectangle has four sides, not two. Always multiply (length + width) by 2 to account for both pairs of opposite sides.

Practice Quiz

Test your knowledge with interactive questions

Look at the rectangle ABCD below.

Side AB is 6 cm long and side BC is 4 cm long.

What is the area of the rectangle?
666444AAABBBCCCDDD

FAQ

Everything you need to know about this question

Why do I multiply by 2 in the perimeter formula?

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A rectangle has four sides: two lengths and two widths. The formula P = 2(l + w) accounts for both pairs of opposite sides that are equal in length.

Can I just add all four sides instead?

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Yes! You can calculate 18 + 2 + 18 + 2 = 40. This gives the same answer as the formula P = 2(18 + 2) = 40, but the formula is usually faster.

What if the rectangle was rotated differently?

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It doesn't matter! Whether the 18 is horizontal or vertical, perimeter stays the same. The formula P = 2(l + w) works for any rectangle orientation.

How do I know which number is length and which is width?

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For perimeter calculations, it doesn't matter which you call length or width! The formula P = 2(a + b) works the same way regardless of which dimension you pick first.

What units should my answer have?

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Since the problem shows dimensions as 18 and 2 without specific units, your answer should just be the number 40. In real problems, use the same units as given (cm, inches, etc.).

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