Forgetting to multiply the length by 2

Oct 13, 2025 by wbrum.org 137 views

Introduction

In mathematics, the perimeter of a rectangle is calculated by adding the lengths of all its sides. Given the length and perimeter of a rectangular dog pen, we can use algebraic equations to find the width of the pen. In this article, we will use the given information to solve for the width of Cooper's dog pen.

Understanding the Problem

The problem states that Cooper built a rectangular dog pen that is 21 feet long and has a perimeter of 78 feet. We need to find the width of the pen. To do this, we will use the formula for the perimeter of a rectangle, which is:

P = 2l + 2w

where P is the perimeter, l is the length, and w is the width.

Given Information

Length (l) = 21 feet
Perimeter (P) = 78 feet

Setting Up the Equation

We can now substitute the given values into the formula for the perimeter of a rectangle:

78 = 2(21) + 2w

Simplifying the Equation

To simplify the equation, we can first multiply 2 by 21:

78 = 42 + 2w

Isolating the Variable

Next, we can subtract 42 from both sides of the equation to isolate the variable w:

36 = 2w

Solving for the Width

Finally, we can divide both sides of the equation by 2 to solve for the width:

w = 36/2 w = 18

Conclusion

Therefore, the width of Cooper's dog pen is 18 feet.

Real-World Applications

This problem has real-world applications in various fields, such as:

Architecture: When designing buildings, architects need to consider the perimeter of the structure to ensure that it is safe and functional.
Engineering: Engineers use perimeter calculations to design and build bridges, roads, and other infrastructure projects.
Landscaping: When designing gardens or parks, landscapers need to consider the perimeter of the area to ensure that it is visually appealing and functional.

Tips and Tricks

When solving for the width of a rectangle, make sure to use the correct formula for the perimeter.
Use algebraic equations to isolate the variable and solve for the width.
Check your work by plugging the solution back into the original equation.

Common Mistakes

Forgetting to multiply the length by 2: When calculating the perimeter, make sure to multiply the length by 2.
Not isolating the variable: When solving for the width, make sure to isolate the variable by subtracting the length from both sides of the equation.
Not checking the solution: When plugging the solution back into the original equation, make sure to check that it is correct.

Additional Resources

For more information on solving for the width of a rectangle, check out the following resources:

Khan Academy: Perimeter and Area of Rectangles
Mathway: Solving for the Width of a Rectangle
IXL: Perimeter and Area of Rectangles

Conclusion

Q: What is the formula for the perimeter of a rectangle?

A: The formula for the perimeter of a rectangle is P = 2l + 2w, where P is the perimeter, l is the length, and w is the width.

Q: How do I solve for the width of a rectangle when given the length and perimeter?

A: To solve for the width of a rectangle when given the length and perimeter, you can use the formula P = 2l + 2w and isolate the variable w by subtracting 2l from both sides of the equation and then dividing both sides by 2.

Q: What if I'm given the width and perimeter, but not the length? Can I still solve for the length?

A: Yes, you can still solve for the length. To do this, you can use the formula P = 2l + 2w and isolate the variable l by subtracting 2w from both sides of the equation and then dividing both sides by 2.

Q: What if I'm given the length and width, but not the perimeter? Can I still solve for the perimeter?

A: Yes, you can still solve for the perimeter. To do this, you can use the formula P = 2l + 2w and substitute the given values for l and w into the equation.

Q: What if I'm given the perimeter and one of the dimensions (either length or width), but not the other dimension? Can I still solve for the other dimension?

A: Yes, you can still solve for the other dimension. To do this, you can use the formula P = 2l + 2w and isolate the variable for the unknown dimension by subtracting 2 times the known dimension from both sides of the equation and then dividing both sides by 2.

Q: What are some common mistakes to avoid when solving for the width of a rectangle?

A: Some common mistakes to avoid when solving for the width of a rectangle include:

Forgetting to multiply the length by 2
Not isolating the variable
Not checking the solution
Not using the correct formula for the perimeter

Q: What are some real-world applications of solving for the width of a rectangle?

A: Some real-world applications of solving for the width of a rectangle include:

Architecture: When designing buildings, architects need to consider the perimeter of the structure to ensure that it is safe and functional.
Engineering: Engineers use perimeter calculations to design and build bridges, roads, and other infrastructure projects.
Landscaping: When designing gardens or parks, landscapers need to consider the perimeter of the area to ensure that it is visually appealing and functional.

Q: How can I practice solving for the width of a rectangle?

A: You can practice solving for the width of a rectangle by using online resources such as Khan Academy, Mathway, or IXL, or by working through practice problems in a textbook or worksheet.

Q: What are some additional resources for learning about solving for the width of a rectangle?

A: Some additional resources for learning about solving for the width of a rectangle include:

Khan Academy: Perimeter and Area of Rectangles
Mathway: Solving for the Width of a Rectangle
IXL: Perimeter and Area of Rectangles
Online textbooks or worksheets
Video tutorials or online courses

Conclusion

In conclusion, solving for the width of a rectangle is a simple process that involves using algebraic equations to isolate the variable. By following the steps outlined in this article and practicing with online resources, you can easily solve for the width of a rectangle and apply this knowledge to real-world problems.