Math Problem Statement

An economy has three industries, farming, building, and clothing. For every dollar of food produced, the farmers use $0.11, the builders use $0.18, and the tailors use $0.06. For every dollar of building, the builders use $0.05, the farmers use $0.07, and the tailors use $0.12. For every dollar of clothing produced, the tailors use $0.15, the builders use $0.18, and the farmers use $0.07. If the external demand for food is $290 million, for building is $170 million, and for clothing is $190 million, what should be the total production for each industry?

Solution

To solve this problem, we need to set up a system of equations that represents the interdependence between the industries: farming, building, and clothing. The external demand for each industry must be satisfied while also considering the intermediate purchases between industries.

Step 1: Define Variables

Let the total production in each industry be represented by the following variables:

  • x1x_1: Total production of food (farming) in millions of dollars.
  • x2x_2: Total production of building in millions of dollars.
  • x3x_3: Total production of clothing in millions of dollars.

Step 2: Set Up the Equations

The total production in each industry is influenced by the demand from external sources and the purchases made by other industries. For each industry, we will write an equation based on the total production of that industry, considering both internal and external demand.

Food (Farming) Equation:

The total demand for food consists of:

  • External demand of $290 million.
  • Purchases made by the builders ($0.18 per dollar of food production) and tailors ($0.06 per dollar of food production).

Thus, the equation for food production is: x1=290+0.11x1+0.07x2+0.07x3x_1 = 290 + 0.11x_1 + 0.07x_2 + 0.07x_3

Building Equation:

The total demand for building consists of:

  • External demand of $170 million.
  • Purchases made by the farmers ($0.07 per dollar of building production) and tailors ($0.18 per dollar of building production).

Thus, the equation for building production is: x2=170+0.18x1+0.05x2+0.12x3x_2 = 170 + 0.18x_1 + 0.05x_2 + 0.12x_3

Clothing Equation:

The total demand for clothing consists of:

  • External demand of $190 million.
  • Purchases made by the farmers ($0.06 per dollar of clothing production) and builders ($0.12 per dollar of clothing production).

Thus, the equation for clothing production is: x3=190+0.15x1+0.18x2+0.07x3x_3 = 190 + 0.15x_1 + 0.18x_2 + 0.07x_3

Step 3: Simplify the Equations

We can simplify each equation to isolate the variables on one side.

  1. For Food (Farming): x1=290+0.11x1+0.07x2+0.07x3x_1 = 290 + 0.11x_1 + 0.07x_2 + 0.07x_3 Subtract 0.11x10.11x_1 from both sides: x10.11x1=290+0.07x2+0.07x3x_1 - 0.11x_1 = 290 + 0.07x_2 + 0.07x_3 0.89x1=290+0.07x2+0.07x30.89x_1 = 290 + 0.07x_2 + 0.07x_3 Now divide by 0.89: x1=290+0.07x2+0.07x30.89x_1 = \frac{290 + 0.07x_2 + 0.07x_3}{0.89}

  2. For Building: x2=170+0.18x1+0.05x2+0.12x3x_2 = 170 + 0.18x_1 + 0.05x_2 + 0.12x_3 Subtract 0.05x20.05x_2 from both sides: x20.05x2=170+0.18x1+0.12x3x_2 - 0.05x_2 = 170 + 0.18x_1 + 0.12x_3 0.95x2=170+0.18x1+0.12x30.95x_2 = 170 + 0.18x_1 + 0.12x_3 Now divide by 0.95: x2=170+0.18x1+0.12x30.95x_2 = \frac{170 + 0.18x_1 + 0.12x_3}{0.95}

  3. For Clothing: x3=190+0.15x1+0.18x2+0.07x3x_3 = 190 + 0.15x_1 + 0.18x_2 + 0.07x_3 Subtract 0.07x30.07x_3 from both sides: x30.07x3=190+0.15x1+0.18x2x_3 - 0.07x_3 = 190 + 0.15x_1 + 0.18x_2 0.93x3=190+0.15x1+0.18x20.93x_3 = 190 + 0.15x_1 + 0.18x_2 Now divide by 0.93: x3=190+0.15x1+0.18x20.93x_3 = \frac{190 + 0.15x_1 + 0.18x_2}{0.93}

Step 4: Solve the System of Equations

Now that we have three equations in terms of x1x_1, x2x_2, and x3x_3, we can solve them either by substitution or using matrix methods.

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Math Problem Analysis

Mathematical Concepts

Linear Algebra
System of Equations
Economic Input-Output Model

Formulas

Ax = d (where A is the input-output matrix, x is the production vector, and d is the demand vector)

Theorems

Matrix Inversion Theorem
Gaussian Elimination

Suitable Grade Level

Undergraduate Economics or Advanced High School Math