Theory of Consumer Behaviour

UTILITY

**Utility** is the want-satisfying capacity of a commodity. It is the satisfaction or benefit a consumer derives from consuming a good or service. Utility is **subjective** — different individuals derive different levels of utility from the same commodity based on their preferences, needs, and circumstances. It also varies with **place** and **time**. For example, a heater provides higher utility in Ladakh (cold place) than in Chennai (hot place); a fan provides higher utility in summer than in winter.

Cardinal Utility Analysis

**Cardinal utility analysis** assumes that utility can be measured and expressed numerically. A consumer can quantify satisfaction — e.g., "This shirt gives me 50 units of utility." This approach allows for mathematical analysis of consumer behaviour and demand.

Measures of Utility

**Total Utility (TU)** is the total satisfaction derived from consuming a given quantity of a commodity. If a consumer consumes n units of a commodity, TU increases as consumption increases, but at a diminishing rate.

**Marginal Utility (MU)** is the additional satisfaction gained from consuming one more unit of a commodity, keeping consumption of other goods constant.

**Formula:** MU_n = TU_n − TU_(n−1)

For example: If 4 bananas give 28 units of total utility and 5 bananas give 30 units, then MU of 5th banana = 30 − 28 = 2 units.

**Relationship:** TU_n = MU₁ + MU₂ + ... + MU_n

Total utility is the sum of all marginal utilities up to that unit. TU increases as long as MU is positive, reaches maximum when MU = 0, and decreases when MU becomes negative.

Law of Diminishing Marginal Utility

**Definition:** As consumption of a commodity increases, the marginal utility derived from each additional unit decreases, while consumption of other commodities remains constant.

**Economic Logic:**

After consuming some quantity, the consumer's desire for additional units weakens

Each successive unit provides less additional satisfaction than the previous one

This is because the commodity becomes less scarce relative to the consumer's needs

**Graphical Illustration:** The MU curve slopes downward. As shown in standard example: MU falls from 12 to 6 to 4 to 2 to 0 as consumption increases. When MU = 0, TU is at maximum. When MU becomes negative, TU declines.

**Exam Important Point:** This law explains why demand curves slope downward — as price falls, consumers buy more units, but each additional unit provides less satisfaction, so they won't pay as much for each successive unit.

Derivation of Demand Curve Using Cardinal Utility

**Demand** is the quantity of a commodity a consumer is willing and able to buy at a given price, with other factors constant.

**Demand Curve:** A downward-sloping graphical representation showing the inverse relationship between price and quantity demanded.

**Law of Demand:** As price of a commodity falls, quantity demanded increases; as price rises, quantity demanded falls.

**Explanation via Diminishing MU:**

At high prices, the consumer buys few units where MU is high

As price falls, the consumer buys additional units where MU is lower

The consumer will only buy the 6th unit if price falls below what they paid for the 5th unit

This creates a downward-sloping demand curve

**Example:** If a banana priced at Rs 5 gives MU of 10 units, a consumer buys it. The next banana's MU might be 8 units, so the consumer only buys it if price drops to Rs 4. This inverse price-quantity relationship reflects diminishing marginal utility.

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ORDINAL UTILITY ANALYSIS

**Ordinal utility analysis** does not measure utility numerically. Instead, it **ranks** consumption bundles in order of preference (1st, 2nd, 3rd preferred). The consumer can state whether bundle A is preferred to bundle B, but need not assign specific numbers. This approach is more realistic since consumers rank choices rather than quantify satisfaction.

Indifference Curve

**Definition:** An indifference curve is a curve joining all points (consumption bundles) that give the consumer **equal satisfaction or utility**. The consumer is "indifferent" between any two bundles on the same curve because both provide the same level of satisfaction.

**Notation:** Bundle (x₁, x₂) represents x₁ quantity of good 1 and x₂ quantity of good 2. For example, bundle (5, 10) = 5 bananas and 10 mangoes.

**Example:** Bundles A(1, 15), B(2, 12), C(3, 10), D(4, 9) all lie on the same indifference curve, meaning all four combinations give the same total utility to the consumer.

**Graphical Feature:** Indifference curves are plotted with one good on the horizontal axis and another on the vertical axis. Points A, B, C, D on an indifference curve are equidistant in satisfaction terms.

Marginal Rate of Substitution (MRS)

**Definition:** MRS is the rate at which a consumer will substitute one commodity for another while maintaining the same level of utility (staying on the same indifference curve).

**Formula:** MRS = |ΔY/ΔX|

This represents how many units of good Y the consumer is willing to give up to get one additional unit of good X.

**Interpretation:**

MRS of 3:1 means the consumer will give up 3 units of Y to gain 1 unit of X

MRS is measured as the absolute value (magnitude) of the slope of the indifference curve

The negative slope of the IC ensures MRS is positive

**Example:** From Table 2.2:

A to B: Consumer gives up 3 mangoes for 1 banana → MRS = 3:1

B to C: Consumer gives up 2 mangoes for 1 banana → MRS = 2:1

C to D: Consumer gives up 1 mango for 1 banana → MRS = 1:1

Law of Diminishing Marginal Rate of Substitution

**Definition:** As consumption of one commodity increases, the consumer's willingness to sacrifice units of another commodity **decreases**, moving along the same indifference curve.

**Economic Logic:**

As the consumer gets more of good X, the MU of X falls

As the consumer has less of good Y, the MU of Y rises

The consumer becomes less willing to trade X for Y

Therefore, MRS falls as we move down and right along an indifference curve

**Graphical Evidence:** The indifference curve becomes **flatter** as we move right — the slope decreases in magnitude, showing decreasing willingness to substitute.

**Example:** Going from A→B→C→D on a banana-mango curve, consumer sacrifices 3, then 2, then 1 mango for each additional banana. The sacrifice decreases progressively.

**Cause:** This law arises because:

MU of bananas falls as quantity of bananas increases

MU of mangoes rises as quantity of mangoes decreases

So the ratio MU_banana/MU_mango falls, which equals MRS

Shape of Indifference Curve

**Standard Shape:** **Convex to the origin** — curves outward from the origin. This shape reflects the law of diminishing MRS.

**Rationale:**

At point A (many mangoes, few bananas), MRS is steep (high) — consumer willing to give up many mangoes

At point D (few mangoes, many bananas), MRS is flat (low) — consumer willing to give up few mangoes

This changing slope creates convexity

**Special Case — Perfect Substitutes:** When two goods can be used interchangeably with identical utility (e.g., Rs 5 coin and Rs 5 note), the indifference curve is a **straight line** because MRS remains constant.

**Example:** A consumer will always exchange 1 five-rupee coin for 1 five-rupee note regardless of how many notes they have. Therefore, the IC is linear with constant slope.

Features of Indifference Curves

**1. Downward Slope (Negative Slope):**

If quantity of X increases (ΔX > 0), quantity of Y must decrease (ΔY < 0) to stay on the same curve

Reflects that to have more of one good while maintaining satisfaction, the consumer must have less of the other

Assumption: Both goods have positive marginal utility

**2. Higher Indifference Curves Represent Greater Utility:**

A curve located above and to the right represents bundles with more of at least one commodity and no less of the other

**Monotonic Preferences:** A rational consumer always prefers more of a good (assuming positive MU)

Example: Bundle C(3, 10) is preferred to B(2, 10) — same mangoes but more bananas

**3. Indifference Curves Never Intersect:**

**Proof by Contradiction:**

Suppose IC₁ and IC₂ intersect at point A

Let B lie on IC₁ (with A), and C lie on IC₂ (with A)

Then: U(A) = U(B) from IC₁, and U(A) = U(C) from IC₂

This implies U(B) = U(C), but bundle B has more of at least one good than C

This contradicts monotonic preferences

Therefore, curves cannot intersect

**Exam Important:** These properties ensure a well-defined preference system where the consumer can consistently rank bundles.

Indifference Map

**Definition:** An **indifference map** is a family or set of multiple indifference curves representing all possible preferences of a consumer over different bundles.

**Properties:**

Each IC represents a different level of satisfaction

Higher ICs (further from origin) represent higher utility levels

ICs do not intersect and do not touch

Dense enough to pass through any given bundle

Provides complete representation of consumer preferences

**Interpretation:** The indifference map shows the consumer's complete preference ordering over all possible consumption combinations.

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THE CONSUMER'S BUDGET

A consumer has limited income and faces market prices for goods. Not all consumption bundles are affordable — only those within the budget constraint can be purchased.

Budget Set and Budget Line

**Given:**

Consumer income: M

Price of good 1 (bananas): p₁

Price of good 2 (mangoes): p₂

Quantities: x₁ and x₂

**Budget Constraint Equation:**

p₁·x₁ + p₂·x₂ ≤ M

The consumer can afford any bundle where total spending ≤ income.

**Budget Line (or Budget Constraint):** Bundles where spending exactly equals income:

p₁·x₁ + p₂·x₂ = M

This is a straight line representing all combinations the consumer can afford while spending entire income.

**Budget Set:** All bundles satisfying p₁·x₁ + p₂·x₂ ≤ M — the area below and on the budget line (feasible region).

Graphical Representation

**Axes:** Good 1 (x₁) on horizontal axis, Good 2 (x₂) on vertical axis.

**Intercepts:**

**Horizontal intercept (x₁ axis):** Set x₂ = 0 → x₁ = M/p₁

This is the maximum quantity of good 1 the consumer can buy if spending entire income on it

**Vertical intercept (x₂ axis):** Set x₁ = 0 → x₂ = M/p₂

This is the maximum quantity of good 2 the consumer can buy if spending entire income on it

**Slope of Budget Line:**

Rearranging p₁·x₁ + p₂·x₂ = M for x₂:

x₂ = (M/p₂) − (p₁/p₂)·x₁

**Slope = −p₁/p₂** (negative slope, downward from left to right)

The slope is the **price ratio** — it shows how many units of good 2 must be sacrificed to get one additional unit of good 1.

**Example:**

Income M = Rs 100

Price of banana (p₁) = Rs 5

Price of mango (p₂) = Rs 10

Budget line: 5x₁ + 10x₂ = 100

Intercepts:

If x₂ = 0: x₁ = 20 bananas (spend entire income on bananas)

If x₁ = 0: x₂ = 10 mangoes (spend entire income on mangoes)

Slope = −5/10 = −0.5 (sacrifice 0.5 mangoes for 1 banana)

Effects of Changes in Budget Parameters

**1. Change in Income (M):**

If income increases with prices constant → Budget line shifts **outward (rightward)** parallel to original line

If income decreases → Budget line shifts **inward (leftward)** parallel to original line

Intercepts change but slope remains the same (slope depends only on price ratio)

**2. Change in Relative Prices:**

**If p₁ increases (price of good 1 rises):**

Horizontal intercept: M/p₁ decreases (can buy fewer units of good 1)

Vertical intercept: M/p₂ unchanged (quantity of good 2 unaffected)

Slope: |p₁/p₂| increases in magnitude (steeper line)

Budget line rotates inward around the y-intercept

**If p₂ increases (price of good 2 rises):**

Horizontal intercept: M/p₁ unchanged

Vertical intercept: M/p₂ decreases

Slope: |p₁/p₂| decreases in magnitude (flatter line)

Budget line rotates inward around the x-intercept

**Proportional Change in Both Prices:**

If both p₁ and p₂ increase by the same percentage with M constant → Budget line shifts inward parallel to original

Real purchasing power decreases but price ratio remains unchanged

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CONSUMER EQUILIBRIUM

**Consumer equilibrium** is the situation where the consumer maximizes satisfaction (utility) given their income and market prices. At equilibrium, the consumer chooses the consumption bundle that provides the highest possible utility.

Equilibrium Condition (Ordinal Approach)

At consumer equilibrium using indifference curve analysis:

**IC is tangent to the budget line**

At the point of tangency:

**Slope of IC = Slope of Budget Line**

**MRS = p₁/p₂**

**Economic Interpretation:**

**MRS** = Rate at which consumer is willing to substitute good 1 for good 2

**p₁/p₂** = Rate at which market allows substitution (price ratio)

At equilibrium, willingness to substitute = market's rate of substitution

No incentive to alter the consumption bundle

**Graphical Representation:**

Indifference curve IC* is tangent to budget line BL

Point of tangency E is the equilibrium bundle (x₁*, x₂*)

Any other affordable bundle lies on a lower indifference curve (lower utility)

Two-Commodity Case

Suppose consumer is choosing between bananas (good 1) and mangoes (good 2).

**Equilibrium Condition:**

MRS_(banana for mango) = p_banana/p_mango

If MRS = 2, it means consumer will give up 2 mangoes for 1 banana.

If p_banana/p_mango = 2 (banana costs twice as much), equilibrium is achieved.

**Example:**

If banana costs Rs 10 and mango costs Rs 5 → Price ratio = 10/5 = 2

If consumer's MRS = 2 (willing to give up 2 mangoes for 1 banana) → Equilibrium

If consumer's MRS = 3 (willing to give up 3 mangoes) → Not equilibrium

Consumer would buy more bananas and fewer mangoes until MRS falls to 2

Equilibrium Condition (Cardinal Utility Approach)

In cardinal utility analysis, equilibrium for **single commodity**:

**MU = Price (in terms of money)**

More precisely: **MU/P = MU of money (constant)**

This means the last rupee spent on each commodity gives equal satisfaction.

**For two commodities:**

**MU₁/p₁ = MU₂/p₂ = MU of money**

This condition states that marginal utility per rupee spent must be equal across all goods.

**Interpretation:**

If MU₁/p₁ > MU₂/p₂: Consumer gets more satisfaction per rupee from good 1

Should spend more on good 1, less on good 2

This continues until the ratio equalizes

If MU₁/p₁ = MU₂/p₂: Consumer is satisfied; no incentive to change

**Example:**

MU of banana = 20, price = Rs 5 → MU/P = 20/5 = 4 units per rupee

MU of mango = 15, price = Rs 5 → MU/P = 15/5 = 3 units per rupee

Since 4 > 3, consumer should buy more bananas until MU of banana falls and equality is achieved

Conditions for Equilibrium Summary

**Ordinal Approach (Standard CBSE Board Approach):**

**MRS = p₁/p₂**

IC tangent to budget line

No incentive to substitute goods given market prices

**Cardinal Approach (Alternative):**

**MU₁/p₁ = MU₂/p₂**

Marginal utility per rupee equal across goods

Maximizes total satisfaction given budget

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DEMAND: MEANINGS AND DETERMINANTS

Demand Definition

**Demand** for a commodity is the quantity that a consumer is willing to buy and is able to afford, given:

The price of that commodity

Prices of related commodities

Consumer's income

Consumer's tastes and preferences

**Demand is at a particular price** — it is not a single quantity but a schedule showing quantities demanded at different prices.

Law of Demand

**Statement:** As the price of a commodity falls, the quantity demanded increases (assuming other factors remain constant). Conversely, as price rises, quantity demanded falls.

**Graphical Representation:** The demand curve slopes downward from left to right.

**Axes:** Quantity (Q) on horizontal axis, Price (P) on vertical axis.

**Formula (Slope):** The slope of demand curve is negative: ΔQ/ΔP < 0

Reasons for Downward-Sloping Demand Curve

**1. Substitution Effect:**

When price of commodity X falls, it becomes cheaper relative to substitute goods

Consumer substitutes X for other goods, increasing quantity demanded of X

Example: If banana price falls while mango price is constant, bananas become relatively cheaper; consumers buy more bananas and fewer mangoes

**2. Income Effect:**

When price of commodity X falls, the consumer's real income (purchasing power) increases

With higher real income, consumer demands more of normal goods

Example: If grocery prices fall, consumer's budget goes further; they can buy more groceries overall

**3. Diminishing Marginal Utility (Cardinal Explanation):**

At high prices, consumer buys only units with high marginal utility

As price falls, consumer buys additional units with lower marginal utility

Consumer only willing to buy additional units at lower prices

This creates negative relationship between price and quantity

Movement Along Demand Curve vs. Shifts in Demand Curve

**Movement Along Demand Curve:**

Caused by **change in own price** of the commodity

Movement along the same curve

**Upward movement (left):** Price increase → Quantity demanded decreases

**Downward movement (right):** Price decrease → Quantity demanded increases

**Shifts in Demand Curve (Change in Demand):**

Caused by changes in **factors other than own price**

Entire curve shifts

**Rightward/outward shift:** Demand increases — more quantity demanded at same price

**Leftward/inward shift:** Demand decreases — less quantity demanded at same price

**Causes of Demand Shifts:**

1. **Change in Income:**

Income increase → Demand for normal goods shifts right (demand ↑)

Income increase → Demand for inferior goods shifts left (demand ↓)

Example: Higher income increases demand for fruits, decreases demand for coarse grains

2. **Change in Price of Related Goods:**

**Substitutes (goods used in place of each other):**

Price of substitute rises → Demand for original good shifts right

Example: If mango price rises, demand for banana increases

**Complements (goods used together):**

Price of complement rises → Demand for original good shifts left

Example: If bread price rises, demand for butter may decrease

3. **Change in Consumer Tastes/Preferences:**

Preference shift toward a good → Demand increases (right shift)

Preference shift away → Demand decreases (left shift)

Example: Health awareness increases demand for salads, decreases demand for junk food

4. **Change in Consumer Expectations:**

Expected price increase → Current demand increases (buy now before price rises)

Expected income increase → Current demand for normal goods may increase

Example: Monsoon prediction affects agricultural commodity demand

5. **Change in Number of Consumers:**

More consumers in market → Market demand increases

Fewer consumers → Market demand decreases

Example: Migration increases demand in destination city

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ELASTICITY OF DEMAND

**Elasticity of demand** measures the **responsiveness** of quantity demanded to changes in price, income, or prices of related goods. It quantifies how sensitive demand is to various factors.

Price Elasticity of Demand (PED)

**Definition:** Price elasticity of demand measures the percentage change in quantity demanded resulting from a 1% change in price.

**Formula:**

E_d = (% Change in Quantity Demanded)/(% Change in Price)

E_d = (ΔQ/Q)/(ΔP/P) = (ΔQ/ΔP) × (P/Q)

Where:

ΔQ = change in quantity demanded

ΔP = change in price

Q = original quantity

P = original price

**Interpretation:**

E_d > 1: **Elastic demand** — quantity demanded is highly responsive to price change

1% price change → >1% quantity change

Consumer demand changes significantly with price

E_d = 1: **Unit elastic demand** — percentage change in quantity equals percentage change in price

1% price change → 1% quantity change

E_d < 1: **Inelastic demand** — quantity demanded is not very responsive to price change

1% price change → <1% quantity change

Consumer demand changes less than proportionately with price

E_d = 0: **Perfectly inelastic demand** — quantity demanded doesn't change with price (vertical curve)

E_d = ∞: **Perfectly elastic demand** — any price change causes infinite quantity response (horizontal curve)

**Sign Convention:** Price elasticity is negative (since P and Q move in opposite directions per law of demand), but often reported as absolute value.

Factors Affecting Price Elasticity of Demand

**1. Nature of the Commodity:**

**Necessities** (salt, basic grains, medicines): Inelastic — demand relatively fixed regardless of price

**Luxuries** (jewelry, vacation, branded goods): Elastic — demand highly responsive to price changes

Example: Demand for insulin is inelastic; demand for gold jewellery is elastic

**2. Availability of Close Substitutes:**

**Many substitutes available:** Elastic demand — consumers easily switch to alternatives

Example: Demand for one brand of coffee is elastic (many alternative brands)

**Few substitutes:** Inelastic demand — consumers cannot easily replace the good

Example: Demand for salt is inelastic (few substitutes)

**3. Proportion of Income Spent:**

**Large proportion of income:** Elastic demand — consumers very conscious of price

Example: Demand for house is elastic; people carefully consider price

**Small proportion of income:** Inelastic demand — price changes have little impact

Example: Demand for pen is inelastic; price changes barely affect quantity bought

**4. Time Period:**

**Short run:** Inelastic demand — consumers adjust slowly to price changes

Example: Short-run demand for petrol is inelastic (people continue commuting)

**Long run:** Elastic demand — consumers adjust more completely

Example: Long-run demand for petrol is elastic (people buy efficient vehicles, change commute patterns)

**5. Complementarity:**

If good is a complement to another widely-used good: More inelastic

Example: Demand for car tyres is relatively inelastic (complement to cars)

Numerical Example

**Calculation:**

Original quantity: Q = 10 units

Original price: P = Rs 5

New quantity: Q' = 15 units

New price: P' = Rs 4

ΔQ = 15 − 10 = 5

ΔP = 4 − 5 = −1

% ΔQ = (5/10) × 100 = 50%

% ΔP = (−1/5) × 100 = −20%

E_d = 50%/(−20%) = −2.5 (or 2.5 in absolute value)

**Interpretation:** Demand is elastic (|E_d| = 2.5 > 1). A 1% price decrease leads to 2.5% increase in quantity demanded.

Income Elasticity of Demand

**Definition:** Income elasticity measures the percentage change in quantity demanded due to 1% change in consumer income.

**Formula:**

E_income = (% Change in Quantity Demanded)/(% Change in Income)

E_income = (ΔQ/Q)/(ΔM/M) = (ΔQ/ΔM) × (M/Q)

**Classification:**

**1. Normal Goods (E_income > 0):**

Quantity demanded increases with income

Examples: Fruits, vegetables, branded goods, entertainment

**Necessities:** Income elasticity positive but < 1 (low responsiveness)

Example: Demand for wheat increases with income, but not proportionately

**Luxuries:** Income elasticity > 1 (high responsiveness)

Example: Demand for holidays increases significantly with income

**2. Inferior Goods (E_income < 0):**

Quantity demanded decreases with income

Examples: Coarse grains, second-hand goods, cheap substitutes

As income rises, consumers switch to superior alternatives

Example: Demand for ragda (cheap food) falls as income rises

**3. Necessities (E_income = 0):**

Quantity demanded unchanged with income changes

Example: Basic salt consumption unaffected by income changes

Cross Elasticity of Demand

**Definition:** Cross elasticity measures the percentage change in quantity demanded of one commodity due to 1% change in price of another commodity.

**Formula:**

E_cross = (% Change in Q_x)/(% Change in P_y)

E_cross = (ΔQ_x/Q_x)/(ΔP_y/P_y) = (ΔQ_x/ΔP_y) × (P_y/Q_x)

**Where:** Q_x = quantity of good x, P_y = price of good y

**Classification:**

**1. Substitutes (E_cross > 0):**

Cross elasticity is positive

If price of good Y increases, demand for substitute good X increases

Example: Banana and mango are substitutes

If mango price ↑ by 10%, banana demand ↑ by, say, 5% (E_cross = 0.5 > 0)

**2. Complements (E_cross < 0):**

Cross elasticity is negative

If price of good Y increases, demand for complementary good X decreases

Example: Bread and butter are complements

If bread price ↑ by 10%, butter demand ↓ by, say, 5% (E_cross = −0.5 < 0)

**3. Unrelated Goods (E_cross = 0):**

Change in price of one good doesn't affect demand for the other

Example: Shoe price changes don't affect coffee demand

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PRODUCTION AND COSTS (QUANTITATIVE FOUNDATION)

Note: This section provides numerical understanding essential for consumer behaviour analysis related to production decisions.

Production Function

**Definition:** A production function shows the maximum quantity of output that can be produced with given quantities of inputs.

**Notation:**

TP = Total Product (total output produced)

AP = Average Product (output per unit of input) = TP/Input

MP = Marginal Product (additional output from one more unit of input) = ΔTP/ΔInput

**Relationships:**

AP = TP/L (where L = units of labour)

MP = ΔTP/ΔL (change in TP divided by change in labour)

**Numerical Example:**

| Labour | TP | AP | MP |

|--------|----|----|-----|

| 1 | 10 | 10 | 10 |

| 2 | 25 | 12.5 | 15 |

| 3 | 45 | 15 | 20 |

| 4 | 60 | 15 | 15 |

| 5 | 70 | 14 | 10 |

AP = TP/L (at L=3: AP = 45/3 = 15)

MP = Change in TP (from L=2 to L=3: MP = 45−25 = 20)

Law of Variable Proportions

**Statement:** As quantity of a variable input increases (keeping other inputs fixed), total product initially rises at an increasing rate, then at a decreasing rate, and eventually may decline.

**Three Stages:**

**Stage 1: Increasing Returns (MP rising, TP rising at increasing rate)**

MP increases as input increases

TP increases rapidly

AP increases

Example: First 3 workers produce 10, 15, 20 units (MP increasing)

Explanation: Workers cooperate better, specialization increases efficiency

**Stage 2: Decreasing Returns (MP falling but positive, TP rising at decreasing rate)**

MP decreases but remains positive

TP increases but at slower rate

AP still positive but falling

Example: 4th worker adds 15 units, 5th adds 10 units (MP decreasing)

Explanation: Fixed inputs (land, machinery) become proportionally scarcer; coordination becomes difficult

**Stage 3: Negative Returns (MP negative, TP falling)**

MP becomes negative

TP declines

Example: 6th worker may reduce total output

Explanation: Too many workers for fixed resources; overcrowding reduces efficiency

Rational producers never operate here

Cost Concepts

**Fixed Costs (FC):** Costs that don't change with output level

Examples: Rent, insurance, depreciation, salaries of permanent staff

Remains same whether output is 0 or 100 units

TFC (Total Fixed Cost) = constant

**Variable Costs (VC):** Costs that change with output level

Examples: Raw materials, wages of temporary workers, packaging

TVC increases as output increases

At zero output, TVC = 0

**Total Cost (TC):**

**TC = TFC + TVC**

**Average Cost (AC):**

**AC = TC/Q** (cost per unit of output)

Can also be expressed as: **AC = AFC + AVC**

Where:

**AFC = TFC/Q** (Average Fixed Cost)

**AVC = TVC/Q** (Average Variable Cost)

**Marginal Cost (MC):**

**MC = ΔTC/ΔQ** (cost of producing one additional unit)

Can also be calculated as: **MC = ΔTVC/ΔQ** (since TFC doesn't change)

Cost Curves (Shapes and Relationships)

**AFC Curve (Average Fixed Cost):**

Shape: **Rectangular hyperbola** (downward sloping, never touching axes)

As output increases, AFC falls (fixed cost spread over more units)

AFC → 0 as Q → ∞

Example: If TFC = Rs 100, AFC at Q=10 is Rs 10; at Q=20 is Rs 5

**AVC Curve (Average Variable Cost):**

Shape: **U-shaped**

Initially falls due to increasing returns/specialization

Reaches minimum point, then rises due to decreasing returns

Reflects law of variable proportions

**AC Curve (Average Total Cost):**

Shape: **U-shaped**

AC = AFC + AVC

Since AFC always falls and AVC is U-shaped, AC is also U-shaped

Minimum AC occurs at higher output than minimum AVC (because of AFC component)

**MC Curve (Marginal Cost):**

Shape: **U-shaped**

Initially falls (increasing returns, each unit costs less to produce)

Reaches minimum, then rises (decreasing returns, each unit costs more)

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