Complete Unit – Crux
Most important points before solving MCQs
- Demand means quantity buyers are willing and able to buy at different prices during a given time period.
- Demand is more than desire: it needs desire + purchasing power + willingness to spend.
- Quantity demanded is always linked to a price and a time period.
- Law of Demand: other things constant, price and quantity demanded move in opposite directions.
- Demand curve normally slopes downward because of substitution effect, income effect, diminishing marginal utility, new buyers and multiple uses.
- Movement on demand curve happens only because of own price change.
- Shift of demand curve happens because of non-price determinants such as income, tastes, related goods, population or expectations.
- Elasticity measures responsiveness, not just direction of change.
- Price elasticity usually has a negative sign, but for degree of elasticity we generally use the numerical value.
- Cross elasticity sign is very important: positive = substitutes, negative = complements, zero = unrelated goods.
- Income elasticity: positive for normal goods, negative for inferior goods, greater than one for luxury-type goods.
- Advertisement elasticity measures response of demand to advertising expenditure.
1. Why Demand Theory Matters
- Demand and supply are the two basic forces behind market prices and quantities.
- For a business firm, demand tells how much of its product buyers may purchase in a given market and period.
- Managers use demand analysis for pricing, product planning, market entry decisions and estimating future sales.
- The module begins with a business case of green tea to show why firms must understand substitutes, complements, luxury/necessity nature and key demand drivers.
In business terms, demand theory answers: Who will buy, how much, at what price, and why?
2. Meaning of Demand
- Demand means the quantity of a good or service that buyers are ready and capable of purchasing at various prices during a particular period.
- Only wanting a product is not demand. A student may want a luxury car, but it becomes economic demand only if there is ability and willingness to pay.
- Demand is relevant for economic analysis only when it is effective demand.
Essentials of Effective Demand
- Desire for the product
- Means / purchasing power to buy it
- Willingness to use that purchasing power for the product
MCQ Trap
- Desire alone is not demand.
- Demand is always expressed with reference to price and time.
3. Two Important Features of Quantity Demanded
- It is price-related: different prices generally lead to different quantities demanded.
- It is a flow concept: demand must be stated per day, week, month or year; it is not a one-time isolated purchase.
Correct expression: “500 units per month at ₹100 each”, not simply “500 units”.
4. Determinants of Demand
| Determinant | Effect on Demand | Exam Point |
|---|
| Own price | Normally, price rise reduces quantity demanded and price fall increases it. | Basis of Law of Demand. |
| Related goods | Substitutes and complements affect demand differently. | Most tested determinant. |
| Disposable income | Increase in income usually raises demand for normal goods but may reduce demand for inferior goods. | Depends on type of good. |
| Tastes and preferences | Fashion, habits, social influence and brand perception affect demand. | Includes demonstration, bandwagon, snob and Veblen effects. |
| Expectations | Expected future price rise may increase present demand. | Important exception-type logic. |
| Population and composition | Larger population or different age structure changes market demand. | Age mix matters, not only population size. |
| National income and distribution | Higher and more evenly distributed income generally raises consumer demand. | Poor have higher propensity to consume. |
| Credit and interest rates | Easy credit and low interest raise demand, especially for durable goods. | Useful for cars, homes, appliances. |
| Government policy | Taxes reduce demand; subsidies raise demand. | Bans and restrictions reduce demand for undesirable goods. |
5. Related Goods: Complements vs Substitutes
| Type | Meaning | Relationship | Examples |
|---|
| Complementary goods | Goods consumed together. | Price of complement rises → demand for the good falls. | Car and petrol, tea and sugar, pen and ink. |
| Substitute goods | Goods satisfying the same want and usable in place of each other. | Price of substitute rises → demand for the good rises. | Tea and coffee, ink pen and ball pen, toothpaste brands. |
Top Trap
- Complements have inverse relation with price of related good.
- Substitutes have positive relation with price of related good.
6. Income and Types of Goods
- Normal goods: demand increases when consumer income increases.
- Inferior goods: demand may fall after income rises beyond a point.
- Necessaries: demand increases with income, but less than proportionately.
- Luxury / prestige goods: demand generally arises after a higher income level and may increase strongly with income.
For managers, knowing whether the product is normal, inferior, necessity or luxury helps in forecasting demand when income changes.
7. Social Effects on Demand
| Effect | Meaning | Demand Impact |
|---|
| Demonstration effect | People copy consumption behaviour of others. | Demand may rise because others are using it. |
| Bandwagon effect | People buy because many others are buying, to look fashionable or belong to a group. | Demand increases. |
| Snob effect | Some buyers avoid a product when it becomes too common. | Demand decreases for exclusivity-seeking buyers. |
| Veblen effect | High price itself creates prestige value. | Demand may rise when price is high. |
MCQ Trap
- Snob effect is opposite of bandwagon effect.
- Veblen effect is linked to price and prestige.
8. Demand Function
Qx = f(Px, Y, Pr)
- Qx = quantity demanded of commodity X
- Px = own price of commodity X
- Y = money income of the consumer
- Pr = price of related goods
- A specific linear demand function may be written as Q = a - bP.
In this unit, demand is mainly studied as a function of price, while other factors are assumed constant.
9. Law of Demand
- The law explains the relationship between price and quantity demanded.
- Other things remaining constant, when price rises, quantity demanded falls; when price falls, quantity demanded rises.
- This inverse relationship works only under the ceteris paribus assumption.
Price ↑ → Quantity Demanded ↓ | Price ↓ → Quantity Demanded ↑
Assumption Trap
- Income, tastes, prices of related goods and other demand factors must remain unchanged.
- If those factors change, the price-demand relationship may not appear in the usual way.
10. Demand Schedule and Demand Curve
- A demand schedule is a table showing quantities buyers would purchase at different prices per unit of time.
- A demand curve is the graphical presentation of the demand schedule.
- Price is shown on the vertical axis and quantity demanded on the horizontal axis.
- The demand curve normally slopes downward from left to right.
- The slope of demand curve is negative and can be written as - ΔP / ΔQ.
- Demand curves may be straight lines or curved; linear curves are used for simple analysis.
11. Individual Demand and Market Demand
- Individual demand refers to demand by one buyer.
- Market demand is the total quantity demanded by all buyers in the market at each price.
- Market demand schedule is obtained by adding individual quantities demanded at each price.
- Market demand curve is obtained by horizontal summation of individual demand curves.
If A demands 3 units and B demands 2 units at price ₹0, market demand is 5 units.
12. Why Demand Curve Slopes Downward
| Reason | Explanation |
|---|
| Substitution effect | When a good becomes cheaper compared to other goods, consumers substitute it for relatively costlier goods. |
| Income effect | A fall in price raises real purchasing power, allowing the consumer to buy more, especially for normal goods. |
| Diminishing marginal utility | Consumers buy additional units only at lower prices because extra satisfaction from each additional unit falls. |
| New consumers | Lower prices bring in buyers who could not afford the product earlier. |
| Different uses | A lower price encourages wider uses of goods with multiple uses, such as electricity or milk. |
Important Detail
- Substitution effect of a price fall is always positive.
- For inferior goods, income effect may work opposite to substitution effect.
13. Exceptions to the Law of Demand
| Exception | Meaning | Example / Exam Point |
|---|
| Conspicuous goods | Goods demanded for prestige; high price may increase attractiveness. | Veblen effect; diamonds, luxury cars, jewellery. |
| Giffen goods | Inferior goods where price rise may increase demand because income effect is very strong. | All Giffen goods are inferior, but all inferior goods are not Giffen goods. |
| Conspicuous necessities | Goods that become necessary due to social usage or demonstration effect. | Television, refrigerator, air-conditioner-type examples in module. |
| Future price expectations | If buyers expect higher future prices, present demand may rise despite current price rise. | Food grains during expected shortage. |
| Incomplete information / irrational behaviour | Consumers may not know market conditions or may buy impulsively. | Assumption of rational consumer fails. |
| Necessaries | Minimum consumption continues despite price change. | Demand does not fall much. |
| Speculative goods | Rising prices may attract more buyers due to expectation of further gain. | Stocks and shares. |
14. Expansion and Contraction of Demand
- Expansion and contraction happen due to change in own price only, while other factors remain constant.
- Expansion of demand: price falls and quantity demanded rises; movement downward along the same demand curve.
- Contraction of demand: price rises and quantity demanded falls; movement upward along the same demand curve.
Expansion / Contraction = Movement on the same demand curve
15. Increase and Decrease in Demand
- Increase or decrease in demand happens because of non-price determinants.
- Increase in demand: more is demanded at every price; demand curve shifts right.
- Decrease in demand: less is demanded at every price; demand curve shifts left.
| Change | Cause | Curve Effect |
|---|
| Expansion | Own price falls | Downward movement on same curve |
| Contraction | Own price rises | Upward movement on same curve |
| Increase in demand | Favourable non-price factor | Rightward shift |
| Decrease in demand | Unfavourable non-price factor | Leftward shift |
Most Important Trap
- Change in quantity demanded = movement.
- Change in demand = shift.
Demand – Quick Lock
Revise before moving to elasticity
- Demand = desire + ability + willingness + time.
- Own price change causes movement.
- Other factors cause shift.
- Complements move opposite; substitutes move together.
- Giffen, Veblen, speculative goods and expectations are favourite exception areas.
16. Meaning of Elasticity of Demand
- Elasticity of demand means the degree of responsiveness of quantity demanded to a change in one of its determinants.
- It measures how much demand responds, not merely whether it rises or falls.
Main Types
- Price elasticity of demand
- Income elasticity of demand
- Cross elasticity of demand
- Advertisement elasticity of demand
17. Price Elasticity of Demand
Ep = % change in quantity demanded / % change in price
- Price elasticity measures the responsiveness of quantity demanded to a change in own price.
- Because price and demand normally move in opposite directions, price elasticity usually carries a negative sign.
- For classifying degree of elasticity, the numerical value is generally used.
Ep = (ΔQ / Q) ÷ (ΔP / P) = (ΔQ / ΔP) × (P / Q)
18. Methods of Measuring Price Elasticity
| Method | Used For | Key Formula / Logic |
|---|
| Percentage method | Direct calculation from percentage changes. | % change in Q / % change in P. |
| Point elasticity | Elasticity at a specific point on demand curve. | Lower segment / upper segment on a linear demand curve. |
| Arc elasticity | Elasticity between two points on a demand curve. | Uses average of old and new price/quantity. |
| Total outlay method | Judging elasticity from change in total expenditure. | Compares price movement with total spending. |
19. Point Elasticity on Linear Demand Curve
- Point elasticity measures elasticity at one particular point on the demand curve.
- On a straight-line demand curve, elasticity differs at different points.
- Upper portion is generally elastic, middle point is unitary, and lower portion is inelastic.
Point Elasticity = Lower segment of demand curve / Upper segment of demand curve
20. Arc Elasticity
- Arc elasticity measures elasticity over a range between two points of a demand curve.
- It is useful when price change is not very small.
- It avoids different answers that may arise depending on whether the old or new base is used.
Arc Ep = (ΔQ / ΔP) × [(P1 + P2) / (Q1 + Q2)]
21. Degrees of Price Elasticity
| Value | Name | Meaning | Curve Idea |
|---|
| Ep = 0 | Perfectly inelastic | Quantity does not change at all with price. | Vertical demand curve. |
| Ep < 1 | Inelastic | Quantity changes less than proportionately. | Steep curve. |
| Ep = 1 | Unitary elastic | Quantity and price change in same proportion. | Rectangular hyperbola logic for constant unit elasticity. |
| Ep > 1 | Elastic | Quantity changes more than proportionately. | Flatter curve. |
| Ep = ∞ | Perfectly elastic | Small price change causes very large / unlimited change in demand. | Horizontal demand curve. |
22. Total Outlay Method
- Total outlay / total expenditure means Price × Quantity purchased.
- This method studies how total expenditure changes when price changes.
| Price Change | Total Expenditure Behaviour | Elasticity |
|---|
| Price falls | Total expenditure rises | Elastic demand |
| Price falls | Total expenditure falls | Inelastic demand |
| Price changes | Total expenditure remains same | Unitary elastic demand |
| Price rises | Total expenditure falls | Elastic demand |
| Price rises | Total expenditure rises | Inelastic demand |
Scoring Area
- Elastic demand: price and total expenditure move in opposite directions.
- Inelastic demand: price and total expenditure move in same direction.
23. Total Revenue and Elasticity
- Total revenue of the seller equals price multiplied by quantity sold.
- For a buyer, the same amount is total expenditure.
- If demand is elastic, reducing price can increase total revenue.
- If demand is inelastic, increasing price can increase total revenue.
- If demand is unitary elastic, total revenue remains unchanged when price changes.
24. Determinants of Price Elasticity
| Factor | Effect on Elasticity | Example / Logic |
|---|
| Availability of substitutes | More substitutes → more elastic demand. | Brands of soap/toothpaste; petrol as a group is inelastic, a brand may be elastic. |
| Share in consumer budget | Higher budget share → more elastic. | Rent/clothing more elastic than salt/buttons. |
| Nature of need | Necessities inelastic; luxuries elastic. | Food/housing vs home theatre. |
| Number of uses | More uses → more elastic. | Milk can be used for curd, cream, ghee, sweets. |
| Time period | Longer time → more elastic. | Consumers adjust habits or find substitutes over time. |
| Consumer habits | Strong habits → inelastic demand. | Habitual consumption reduces price sensitivity. |
| Tied demand | Demand tied to another product is normally inelastic. | Printer and ink cartridges. |
| Price range | Very high and very low price range goods tend to be inelastic. | Middle range goods often more elastic. |
| Minor complementary items | Cheap complements of costly goods tend to be inelastic. | Small accessories used with expensive products. |
25. Importance of Price Elasticity
- Helps business managers decide whether price changes will increase or reduce total revenue.
- Helps firms design pricing strategy for profit maximisation.
- Helps government set prices of public services such as transport and telecom.
- Helps government estimate tax revenue effects when indirect taxes are imposed.
- Governments often tax goods with relatively inelastic demand, such as alcohol and tobacco, because demand falls less.
26. Income Elasticity of Demand
- Income elasticity measures the responsiveness of demand to change in consumer income.
- It helps businesses forecast sales as average income changes over time.
Ei = % change in demand / % change in income
Ei = (ΔQ / Q) ÷ (ΔY / Y) = (ΔQ / ΔY) × (Y / Q)
| Value | Type of Good | Meaning |
|---|
| Ei > 1 | Income elastic / luxury-type | Demand rises faster than income. |
| Ei = 1 | Unit income elastic | Demand rises in same proportion as income. |
| 0 < Ei < 1 | Income inelastic necessity | Demand rises slower than income. |
| Ei < 0 | Inferior good | Demand falls when income rises. |
27. Cross-Price Elasticity of Demand
- Cross elasticity measures how demand for one good responds to change in price of another related good.
- Here, the sign of elasticity is important because it identifies the relationship between goods.
Ec = % change in quantity demanded of X / % change in price of Y
Ec = (ΔQx / Qx) ÷ (ΔPy / Py) = (ΔQx / ΔPy) × (Py / Qx)
| Value / Sign | Relation | Interpretation |
|---|
| Positive | Substitutes | Price of Y rises, demand for X rises. |
| Negative | Complements | Price of Y rises, demand for X falls. |
| Zero | Unrelated goods | Price change of Y has no effect on demand for X. |
| Infinity | Perfect substitutes | Very high substitutability. |
MCQ Trap
- For cross elasticity, do not ignore the sign.
- Higher positive value means closer substitutes.
- More negative value means stronger complements.
28. Advertisement Elasticity
- Advertisement elasticity, also called promotional elasticity, measures responsiveness of demand to changes in advertising expenditure.
- It helps a business judge whether advertising is actually creating additional sales.
- It is normally positive and may vary from zero to infinity.
Ea = % change in quantity demanded / % change in advertising expenditure
| Value | Interpretation |
|---|
| Ea = 0 | Demand does not respond to additional advertisement. |
| 0 < Ea < 1 | Demand increases less than proportionately to ad spending. |
| Ea = 1 | Demand increases in same proportion as ad spending. |
| Ea > 1 | Demand increases more than proportionately to ad spending. |
Final 1-Min Master Revision
Last scan before MCQs
- Demand must have desire, ability and willingness.
- Law of Demand works under ceteris paribus.
- Movement = own price; shift = other factors.
- Market demand curve = horizontal summation of individual demand curves.
- Substitution effect + income effect explain price effect.
- Giffen goods: all Giffen goods are inferior, but all inferior goods are not Giffen goods.
- Price elasticity: degree matters, usually ignore negative sign for classification.
- Total outlay method is a quick MCQ shortcut.
- Cross elasticity sign is critical: + substitute, - complement.
- Advertisement elasticity checks effectiveness of advertising expenditure.
