Microeconomics Chapter 7: Costs – Study Notes

Costs in Microeconomics

The Nature of Costs

Understanding the nature of costs is essential for firms aiming to maximize profit. Economists and accountants measure costs differently, with economists considering both explicit and implicit costs, while accountants focus on explicit costs for financial reporting.

• Explicit Costs: Direct, out-of-pocket payments for inputs (e.g., wages, materials).

• Implicit Costs: The value of forgone opportunities (e.g., income from alternative uses of resources).

• Economic (Opportunity) Cost: The value of the best alternative use of a resource, including both explicit and implicit costs.

• Sunk Cost: A past expenditure that cannot be recovered and should not affect current production decisions.

Example: If a manager attends a free seminar but forgoes a talk valued at $100 (costing $40), the opportunity cost is $60 (=$100−$40).

Costs of Durable Inputs

Durable goods are inputs usable for several years. Measuring their cost involves:

• Allocating the purchase cost over time (depreciation).

• Adjusting for changes in the value of capital over time.

Sunk Costs

Sunk costs are expenditures that cannot be recovered. They are not relevant for current production decisions and are not considered opportunity costs.

Short-Run Costs

Types of Short-Run Costs

• Fixed Cost (F): Costs that do not vary with output (e.g., rent).

• Variable Cost (VC): Costs that change with the quantity produced (e.g., raw materials).

• Total Cost (C): The sum of fixed and variable costs.

Formula:

$C = F + VC$

Marginal and Average Costs

• Marginal Cost (MC): The extra cost of producing one more unit of output.

• Average Fixed Cost (AFC): Fixed cost per unit of output.

• Average Variable Cost (AVC): Variable cost per unit of output.

• Average Cost (AC): Total cost per unit of output.

Formulas:

$MC = \frac{\Delta C}{\Delta q} = \frac{\Delta VC}{\Delta q}$

$AFC = \frac{F}{q}$

$AVC = \frac{VC}{q}$

$AC = \frac{C}{q}$

Relationship Between Average and Marginal Cost Curves

• When MC < AC, AC is falling.

• When MC > AC, AC is rising.

• MC intersects AC and AVC at their minimum points.

Effects of Taxes on Costs

• Specific Tax: Increases variable and marginal costs by a fixed amount per unit.

• Lump-Sum Tax: Increases fixed cost but does not affect marginal cost.

Example: A $10 per unit tax shifts the MC and AC curves upward by $10.

Long-Run Costs

Long-Run Cost Structure

In the long run, all inputs are variable and fixed costs are avoidable ($F = 0$). The firm can adjust all factors of production to minimize cost for any output level.

Long-Run Total Cost:

$C = wL + rK$

where $w$ is the wage rate, $L$ is labor, $r$ is the rental rate of capital, and $K$ is capital.

Isocost Lines

An isocost line shows all combinations of labor and capital that cost the same total amount.

Isocost Equation:

$wL + rK = C$

Solve for $K$:

$K = \frac{C}{r} - \frac{w}{r}L$

Table: Bundles of Labor and Capital That Cost $200

Labor (L)	Capital (K)
0	25
5	20
10	15
15	10
20	5
25	0

Additional info: Table inferred from the isocost equation with w = r = 8 for illustration.

Cost Minimization Rules

• Lowest-Isocost Rule: Choose the input bundle on the lowest isocost line that touches the isoquant for the desired output.

• Tangency Rule: Cost is minimized where the isoquant is tangent to the isocost line.

• Last-Dollar Rule: The last dollar spent on each input yields the same marginal product per dollar.

Mathematical Condition for Cost Minimization:

$\frac{MP_L}{w} = \frac{MP_K}{r}$

where $MP_L$ and $MP_K$ are the marginal products of labor and capital, respectively.

Expansion Path and Long-Run Cost Function

• Expansion Path: The locus of cost-minimizing input combinations as output varies.

• Long-Run Cost Function: Shows the minimum cost of producing each output level when all inputs are variable.

Economies and Diseconomies of Scale

• Economies of Scale: Average cost decreases as output increases.

• Diseconomies of Scale: Average cost increases as output increases.

Table: Returns to Scale and Long-Run Costs

Returns to Scale	Effect on Long-Run Average Cost
Increasing	Decreases
Constant	Constant
Decreasing	Increases

The Learning Curve

• Learning by Doing: Productivity increases as cumulative output increases due to gained experience.

• Learning Curve: Shows the relationship between average cost and cumulative output.

Cost of Producing Multiple Goods

Economies of Scope

• Economies of Scope: It is less expensive to produce two or more goods jointly than separately.

• Production Possibility Frontier (PPF): Shows the maximum output combinations possible from a fixed amount of input.

Example: A factory producing both beer and soft drinks may share bottling facilities, reducing total cost compared to producing each in separate plants.

Summary Table: Key Cost Concepts

Concept	Definition
Explicit Cost	Direct monetary payment for inputs
Implicit Cost	Value of forgone alternatives
Opportunity Cost	Sum of explicit and implicit costs
Sunk Cost	Past expenditure not recoverable
Fixed Cost (F)	Cost that does not vary with output
Variable Cost (VC)	Cost that varies with output
Total Cost (C)	Sum of fixed and variable costs
Marginal Cost (MC)	Cost of producing one more unit
Average Cost (AC)	Total cost per unit of output
Economies of Scale	AC falls as output rises
Diseconomies of Scale	AC rises as output rises
Economies of Scope	Joint production is cheaper than separate

Additional info: Some tables and formulas have been logically reconstructed based on standard microeconomics content and the context provided.