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title: "Theory of Cost Notes for CA Foundation Economics | Meaning, Key Points, Exam Focus | Chanakya Commerce Classes"
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# Theory of Cost
Unit 2 · Chapter 3 · MCQ-focused revision sheet for May 2026 exam onwards
### Crux First
- Cost = Monetary value of resources used .
- Explicit cost vs Implicit cost is very important.
- Accounting cost is not equal to Economic cost .
- Fixed vs Variable cost is the core short-run concept.
- TC = TFC + TVC
- AFC, AVC, ATC and MC relationships are very frequently asked.
- MC cuts ATC and AVC at their minimum point .
- Cost curves mainly follow U-shaped logic .
- Opportunity cost = next best alternative forgone.
- Shutdown point = minimum AVC.
### 1. Meaning of Cost
#### Basic Idea
- Cost means the value of inputs used in production .
- It includes payments made for resources such as labour, materials, land and capital.
#### Examples
- Labour wages
- Raw material
- Rent
- Interest
### 2. Types of Cost
#### 1. Explicit Cost
- Explicit costs are paid in cash .
- They are recorded in the books of accounts .
- Examples: wages, rent, electricity charges.
#### 2. Implicit Cost
- Implicit costs are not paid in cash but represent the opportunity cost of own resources .
- Examples: Rent of own building Owner’s salary
- Rent of own building
- Owner’s salary
### 3. Opportunity Cost
#### Definition
- Opportunity cost is the value of the next best alternative sacrificed .
#### Example
- If a machine is used for Product A instead of Product B, then profit from Product B is the opportunity cost.
#### MCQ Trap
- Opportunity cost is not historical cost.
- It is not accounting cost.
- It is a future-oriented decision concept .
### 4. Fixed Cost vs Variable Cost
#### Fixed Cost (TFC)
- Fixed cost does not change with output .
- It exists even when output is zero.
- Examples: rent, salary of permanent staff.
#### Variable Cost (TVC)
- Variable cost changes with output .
- Examples: raw material, power.
### 5. Short Run Cost Concepts
#### 1. Total Cost (TC)
#### 2. Average Fixed Cost (AFC)
- AFC always falls as output rises.
- Reason: fixed cost gets spread over more units.
#### 3. Average Variable Cost (AVC)
- AVC is generally U-shaped .
#### 4. Average Total Cost (ATC)
#### 5. Marginal Cost (MC)
- Marginal cost mainly depends on change in variable cost , because fixed cost does not change.
### 6. Cost Curve Relationship
#### Most Important MCQ Logic
- MC < ATC → ATC falls
- MC = ATC → ATC is minimum
- MC > ATC → ATC rises
- MC cuts ATC at its minimum point.
- MC cuts AVC at its minimum point.
One of the most repeated ICAI MCQs.
### 7. Shape of Cost Curves
#### Why U-Shape?
- Phase 1: Better efficiency leads to falling cost.
- Phase 2: Diminishing returns lead to rising cost.
- Curve | Shape
- AFC | Always downward
- AVC | U-shaped
- ATC | U-shaped
- MC | U-shaped
### 8. Long Run Cost
- In the long run, all costs are variable .
- There is no fixed cost in the long run.
- Main concept tested here is economies of scale .
#### Types of Economies
- Internal Economies Better machinery Specialisation
- Better machinery
- Specialisation
- External Economies Industry growth Infrastructure development
- Industry growth
- Infrastructure development
#### Diseconomies
- Management issues
- Coordination problems
### 9. Shutdown Point
- A firm continues production if Price ≥ AVC .
- If Price < AVC , the firm should shut down.
#### MCQ Gold Point
- Shutdown point = minimum AVC
- Break-even point = minimum ATC
### 10. Other Important Cost Types
#### 1. Sunk Cost
- Already incurred
- Cannot be recovered
- Should be ignored in decision making
#### 2. Incremental Cost
- Extra cost arising due to a change in decision or output.
#### 3. Replacement Cost
- Cost of replacing an existing asset.
#### 4. Historical Cost
- Original purchase cost of an asset.
### Final Quick Revision
- Economic cost = Explicit + Implicit
- Opportunity cost = next best alternative forgone
- AFC always falls
- MC cuts ATC and AVC at the minimum point
- Shutdown point = Price = AVC
- Break-even point = Price = ATC
- Sunk cost = ignore in decision making
### Theory of Cost notes built for concept clarity and exam recall.
This chapter page is written for CA Foundation Business Economics students who want quick understanding first and revision support later. Use it to revise definitions, logic, distinctions, traps, and answer-writing points before moving to objective practice.
- Meaning, definitions and core concepts in simple language
- Important distinctions and exam-oriented traps
- Quick revision support before classroom tests or self-study
- Direct bridge from theory revision to chapter-wise MCQ practice
### What students should be able to answer after revising this topic.
- Explain the meaning and importance of Theory of Cost.
- Identify the most common conceptual differences linked to this unit.
- Write short exam answers using the right terminology and logic.
- Solve chapter-wise objective questions without confusion on keywords.
#### Related chapters for stronger internal revision
- Theory of Production
- Meaning and Types of Markets
- Supply