Substituting the Relationship into the Cost Equation

Oct 13, 2025 by wbrum.org 138 views

===========================================================

Introduction

The town librarian recently purchased a collection of new-release movies on DVD and classic movies on DVD. The librarian spent a total of $$20$$ dollars on the DVDs. Let's assume that the number of new-release movies is represented by the variable $$x$$, and the number of classic movies is represented by the variable $$y$$. In this article, we will explore the mathematical relationship between the number of new-release movies and classic movies, and how it relates to the total amount spent by the librarian.

The Cost of New-Release and Classic Movies

The cost of each new-release movie is $$2$$ dollars, and the cost of each classic movie is $$1$$ dollar. We can represent the total cost of the new-release movies as $$2x$$, and the total cost of the classic movies as $$y$$. Since the librarian spent a total of $$20$$ dollars, we can set up the equation:

2x + y = 20

The Relationship Between New-Release and Classic Movies

We can also represent the relationship between the number of new-release movies and classic movies using a linear equation. Let's assume that the number of new-release movies is directly proportional to the number of classic movies. We can represent this relationship using the equation:

x = ky

where $$k$$ is a constant of proportionality.

Substituting the Relationship into the Cost Equation

We can substitute the relationship between the number of new-release movies and classic movies into the cost equation:

2x + y = 20

2(ky) + y = 20

2ky + y = 20

Simplifying the Equation

We can simplify the equation by combining like terms:

(2k + 1)y = 20

Solving for y

We can solve for $$y$$ by dividing both sides of the equation by $$(2k + 1)$$:

y = \frac{20}{2k + 1}

Substituting the Value of y into the Relationship Equation

We can substitute the value of $$y$$ into the relationship equation:

x = ky

x = k\left(\frac{20}{2k + 1}\right)

Simplifying the Equation

We can simplify the equation by multiplying both sides by $$(2k + 1)$$:

x(2k + 1) = 20k

Expanding the Equation

We can expand the equation by multiplying both sides by $$(2k + 1)$$:

2kx + x = 20k

Rearranging the Equation

We can rearrange the equation by subtracting $$20k$$ from both sides:

2kx - 20k + x = 0

Factoring the Equation

We can factor the equation by grouping the terms:

(2k + 1)x - 20k = 0

Solving for x

We can solve for $$x$$ by adding $$20k$$ to both sides of the equation:

(2k + 1)x = 20k

Dividing Both Sides by (2k + 1)

We can divide both sides of the equation by $$(2k + 1)$$:

x = \frac{20k}{2k + 1}

Conclusion

In this article, we explored the mathematical relationship between the number of new-release movies and classic movies purchased by the town librarian. We set up a linear equation to represent the relationship between the number of new-release movies and classic movies, and solved for the variables $$x$$ and $$y$$. The results show that the number of new-release movies is directly proportional to the number of classic movies, and that the total cost of the DVDs is $$20$$ dollars.

Final Thoughts

The town librarian's DVD collection is a great example of how mathematics can be applied to real-world problems. By using linear equations and algebraic manipulations, we can gain a deeper understanding of the relationships between variables and make predictions about the behavior of complex systems. Whether you're a math enthusiast or just starting to explore the world of mathematics, this article has shown that math is all around us, and that it can be used to solve problems and make sense of the world.

References

[1] "Algebra and Trigonometry" by Michael Sullivan
[2] "Mathematics for the Nonmathematician" by Morris Kline
[3] "Linear Algebra and Its Applications" by Gilbert Strang

Introduction

In our previous article, we explored the mathematical relationship between the number of new-release movies and classic movies purchased by the town librarian. We set up a linear equation to represent the relationship between the number of new-release movies and classic movies, and solved for the variables $$x$$ and $$y$$. In this article, we will answer some of the most frequently asked questions about the town librarian's DVD collection.

Q&A

Q: What is the total cost of the DVDs purchased by the town librarian?

A: The total cost of the DVDs purchased by the town librarian is $$20$$ dollars.

Q: How many new-release movies can the town librarian purchase with $$20$$ dollars?

A: Let's assume that the cost of each new-release movie is $$2$$ dollars. We can set up the equation:

2x = 20

x = \frac{20}{2}

x = 10

So, the town librarian can purchase $$10$$ new-release movies with $$20$$ dollars.

Q: How many classic movies can the town librarian purchase with $$20$$ dollars?

A: Let's assume that the cost of each classic movie is $$1$$ dollar. We can set up the equation:

y = 20

y = 20

So, the town librarian can purchase $$20$$ classic movies with $$20$$ dollars.

Q: What is the relationship between the number of new-release movies and classic movies?

A: The relationship between the number of new-release movies and classic movies is represented by the equation:

x = ky

where $$k$$ is a constant of proportionality.

Q: How can we determine the value of $$k$$?

A: We can determine the value of $$k$$ by substituting the values of $$x$$ and $$y$$ into the equation:

x = ky

10 = k(20)

k = \frac{10}{20}

k = \frac{1}{2}

So, the value of $$k$$ is $$\frac{1}{2}$$.

Q: What is the significance of the value of $$k$$?

A: The value of $$k$$ represents the rate at which the number of new-release movies increases with respect to the number of classic movies. In this case, the value of $$k$$ is $$\frac{1}{2}$$, which means that for every two classic movies, the town librarian can purchase one new-release movie.

Q: Can we use this model to predict the number of new-release movies and classic movies that the town librarian can purchase with a different budget?

A: Yes, we can use this model to predict the number of new-release movies and classic movies that the town librarian can purchase with a different budget. We can simply substitute the new budget into the equation:

2x + y = 20

and solve for $$x$$ and $$y$$.

Conclusion

In this article, we answered some of the most frequently asked questions about the town librarian's DVD collection. We explored the mathematical relationship between the number of new-release movies and classic movies, and solved for the variables $$x$$ and $$y$$. We also determined the value of $$k$$ and its significance. We hope that this article has provided a better understanding of the town librarian's DVD collection and its mathematical implications.

Final Thoughts

References

[1] "Algebra and Trigonometry" by Michael Sullivan
[2] "Mathematics for the Nonmathematician" by Morris Kline
[3] "Linear Algebra and Its Applications" by Gilbert Strang