CA Foundation · Paper 4 · Business Economics

Theory of Consumer Behaviour

Unit 2 · Chapter 2 · MCQ-focused revision sheet for May 2026 exam onwards

MCQ Priority Concept Clarity Quick Revision

Crux First

What you must remember for MCQs

Utility = satisfaction from consumption.
Marginal utility falls as consumption rises.
Consumer buys till MU = Price.
Consumer Surplus = extra benefit over actual price paid.
Indifference Curve shows consumer preferences.
Consumer equilibrium under IC analysis = MRS = Price Ratio.

1. Human Wants

Meaning

Want means a desire to consume goods or services.

Features of Wants

Wants are unlimited.
Each want is satiable.
Wants are competitive because resources are limited.
Wants may be complementary, like car and fuel.
Wants are subjective and relative.
They depend on income, fashion and habits.

Classification of Wants

Necessaries
- For survival: food, shelter
- For efficiency: education, health
- Conventional: based on social customs
Comforts
- Improve the standard of living
Luxuries
- Not essential and usually expensive

MCQ Trap

The same good can shift category over time depending on income, habits and living standards.

2. Utility

Meaning

Utility means the want satisfying power of a good.
It does not mean moral usefulness.
Utility is psychological and subjective.

Types of Utility Measure

Total Utility (TU) = total satisfaction from all units consumed.
Marginal Utility (MU) = extra satisfaction from one more unit.

TU = Σ MU

MU = ΔTU

3. Relation between TU and MU

When TU rises, MU keeps falling gradually.
When TU is maximum, MU becomes zero.
When TU starts falling, MU becomes negative.

Situation	Result
At first unit	TU = MU
MU falling	TU rises at a decreasing rate
MU = 0	TU is maximum
MU negative	TU falls

4. Law of Diminishing Marginal Utility

Meaning

As a consumer consumes more units of a commodity, the extra satisfaction from each additional unit falls.
Only MU falls. TU does not immediately fall.

Key Logic

Wants are satiable.
Intensity of want reduces with consumption.

Assumptions

Units consumed are the same.
Consumption is continuous.
No change in taste or income.
Units are standard.
Law applies generally, though exceptions exist.

Exceptions

Money
Gold

For some goods, desire may keep rising instead of falling.

5. Consumer Surplus

Meaning

Consumer surplus means the extra benefit that a consumer gets over and above the price actually paid.

Consumer Surplus = Willingness to Pay − Actual Price

Key Concept

It is based on the law of diminishing marginal utility.
The consumer buys till MU = Price.

Graph Insight

Consumer surplus is the area below the demand curve and above the price line.

Effect of Price

Price rises → Consumer surplus falls
Price falls → Consumer surplus rises

Applications

Pricing decisions
Tax policy
Welfare measurement
Price discrimination

Limitations

Utility cannot be measured exactly.
Marginal utility of money may not remain constant.
Difficult to apply perfectly in real life.

6. Indifference Curve Analysis

Indifference curve analysis is more realistic than utility analysis.
The consumer compares combinations of goods, not utility numbers.

Assumptions

Consumer is rational.
Consumer has complete knowledge.
Preferences can be ranked.
Preferences are consistent and transitive.
More is better.

7. Indifference Curve

Meaning

An indifference curve shows all combinations of two goods that give the same level of satisfaction.
The consumer is indifferent between all points on the same curve.
It is also called an iso-utility curve.

8. Marginal Rate of Substitution (MRS)

Meaning

MRS is the rate at which one good is exchanged for another while keeping satisfaction unchanged.

MRS = MUx / MUy

Key Concept

MRS diminishes as the consumer moves down an indifference curve.

Reason: As the consumer gets more of X, desire for additional X falls, so willingness to sacrifice Y also falls.

9. Properties of Indifference Curve

Downward sloping
Convex to the origin
Never intersect each other
Higher indifference curve means higher satisfaction
Do not touch the axes

Special Cases

Perfect substitutes → straight line IC
Perfect complements → L-shaped IC

10. Budget Line

Meaning

Budget line shows all combinations of two goods that the consumer can afford.

PXQX + PYQY = Income

Key Points

Slope of budget line = price ratio
It shows the consumer’s constraint

Changes in Budget Line

Income rises → budget line shifts right
Price changes → slope changes

11. Consumer Equilibrium

Condition

Consumer is in equilibrium where the budget line is tangent to the indifference curve.
At equilibrium:
- MRS = Price Ratio
- MUx / MUy = Px / Py

Meaning

The consumer gets maximum satisfaction.
There is no incentive to change the chosen combination.

Final 1-Minute Revision

Strict exam recall points

MU falls = key law of consumer behaviour.
TU maximum when MU = 0.
Consumer surplus = extra benefit.
Indifference curve = equal satisfaction combinations.
MRS diminishes.
Budget line = affordability line.
Consumer equilibrium = MRS = Px/Py.