Chapter 3: Problem 103
A food company originally sells cereal in boxes with dimensions 10 in. by 7 in. by 2.5 in. To make more profit, the company decreases each dimension of the box by \(x\) inches but keeps the price the same. If the new volume is \(81 \mathrm{in} .{ }^{3}\) by how much was each dimension decreased?
Short Answer
Expert verified
Each dimension was decreased by 1 inch.
Step by step solution
01
- Write the formula for volume
The volume of a box can be found using the formula: \[ V = \text{length} \times \text{width} \times \text{height} \] For the original box, the volume is \[ V_0 = 10 \times 7 \times 2.5 \. \]
02
- Calculate the original volume
Calculate the original volume using the dimensions provided: \[ V_0 = 10 \times 7 \times 2.5 = 175 \text{ in}^3 \]
03
- Set up the equation for the new volume
When each dimension of the box decreases by \(x\) inches, the new dimensions are \[ 10-x \text{ in, } 7-x \text{ in, } 2.5-x \text{ in} \]Set up the new volume equation with the given volume of 81 in³: \[ (10 - x)(7 - x)(2.5 - x) = 81 \]
04
- Simplify the equation
To solve for \(x\), first expand and simplify the left side of the equation. Start by multiplying the first two binomials: \[ (10 - x)(7 - x) = 70 - 17x + x^2 \]Then multiply the result by the third binomial: \[ (70 - 17x + x^2)(2.5 - x) = 175 - 70x + 7x^2 - 2.5x + 17x^2 - x^3 \]Combine like terms to get: \[ -x^3 + 24x^2 - 72.5x + 175 = 81 \]
05
- Solve the cubic equation
Move 81 to the left side of the equation to set it equal to 0: \[ -x^3 + 24x^2 - 72.5x + 94 = 0 \]This is a cubic equation and might be difficult to solve by factorization. Consider using numerical methods or a graphing calculator to approximate the value of \(x\). For this equation, \(x = 1\) is a solution.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
cubic equation
A cubic equation is a polynomial equation of the third degree. It takes the general form: \(ax^3 + bx^2 + cx + d = 0\). In the exercise, after simplifying and rearranging the equation for the new cereal box dimensions, we obtained a cubic equation: \(-x^3 + 24x^2 - 72.5x + 94 = 0\). Cubic equations are generally more complex to solve than quadratic equations because they involve higher-order algebra. Solutions can often be approached using:
Understanding how to solve cubic equations is vital for various algebraic problem-solving scenarios.
- Factorization (harder for more complex polynomials)
- Graphing methods
- Numerical methods
Understanding how to solve cubic equations is vital for various algebraic problem-solving scenarios.
volume of a box
Calculating the volume of a box can be quite straightforward using the formula: \(V = \text{length} \times \text{width} \times \text{height}\). For the original cereal box, we calculated the volume as follows:
- Length: 10 inches
- Width: 7 inches
- Height: 2.5 inches
problem-solving in algebra
Algebra involves solving equations to find unknown variables. In this exercise, the problem necessitated setting up and working through a cubic equation. Here's a quick recap of the problem-solving approach:
- Identify and write down the volume formula
- Calculate the original volume
- Set up the equation for the new volume
- Simplify the equation to form a cubic polynomial
- Solve the cubic equation
dimensions and volume
Dimensions are the measurements that define the size of an object. In this example, we dealt with three dimensions: length, width, and height. When we change the dimensions, it affects the volume. If each dimension of the box is decreased by a value \(x\), the new dimensions become explorations of these reductions:
- Original Length: 10 in
- Original Width: 7 in
- Original Height: 2.5 in
- New Dimensions: (10-x), (7-x), (2.5-x)