Business Economics (1): Questionwise Notes

Paper No. 873 | UPC 2412093502 | B.Com. Semester V DSC

How to use these notes: Each answer is arranged as an exam-ready sequence: meaning → assumptions/conditions → diagram logic → analysis → conclusion. Draw the suggested graph in a 9-mark answer and label every axis, curve, equilibrium, shift and shaded area.

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Q1(a) Demand: meaning and demand schedules

Core meaning

Demand is not mere desire. It is the quantity of a commodity that a consumer is willing and able to buy at a given price, at a given place and during a given period, other things remaining constant.

Essential elements

Law of demand

Other things remaining constant, quantity demanded rises when price falls and falls when price rises:

[

Q_d=f(P_x), \qquad \frac{\Delta Q_d}{\Delta P_x}<0

]

The “other things” include income, tastes, prices of related goods, expectations, population and distribution of income.

Individual demand schedule

It shows quantities demanded by one consumer at alternative prices.

Plot price on the vertical axis and quantity on the horizontal axis. The resulting individual demand curve slopes downward.

Market demand schedule

Market demand is the horizontal summation of all individual demands:

[

Q_D=Q_A+Q_B+Q_C+\cdots

]

Extension/contraction versus increase/decrease

Exam conclusion: Effective demand combines desire, willingness and purchasing power. A demand schedule converts this idea into a price–quantity relationship for an individual or the whole market.

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Q1(b) Complementary goods and cross-elasticity: pen and ink

Relationship

Pen and ink are jointly demanded complementary goods. A rise in the price of pens reduces demand for pens and also reduces demand for ink. Their cross-price elasticity is therefore negative.

Diagram instructions

Draw two panels:

1. In the pen market, show a movement along the pen demand curve from (P_1=10,Q_1=5) to (P_2=20,Q_2=3).

2. In the ink market, keep ink price at ₹5 and shift the demand curve for ink left, reducing quantity from 4 to 2.

Cross-price elasticity

[

E_{xy}=

\frac{%\text{ change in quantity demanded of }Y}

{%\text{ change in price of }X}

]

Taking ink as (Y) and pen as (X), using original values:

[

E_{\text{ink,pen}}

=\frac{(2-4)/4}{(20-10)/10}

=\frac{-0.50}{1}

=-0.50

]

Thus, a 1% increase in the price of pens produces approximately a 0.5% decrease in demand for ink.

If the examiner expects the arc method:

[

E_{xy}=

\frac{\Delta Q_y}{\Delta P_x}

\times

\frac{P_{x1}+P_{x2}}{Q_{y1}+Q_{y2}}

=\frac{-2}{10}\times\frac{30}{6}=-1

]

Both methods give the economically important result: the sign is negative, confirming complementarity. State the method used.

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Q1(c) Price elasticity of demand and methods of measurement

Price elasticity of demand measures the degree of responsiveness of quantity demanded to a change in the commodity’s own price, other factors constant.

[

E_d=\frac{%\Delta Q_d}{%\Delta P}

]

The coefficient is normally negative because price and quantity demanded move inversely; comparisons generally use its absolute value.

Degrees

Methods

1Percentage/proportionate method

[

E_d=\frac{\Delta Q}{Q}\div\frac{\Delta P}{P}

=\frac{\Delta Q}{\Delta P}\times\frac{P}{Q}

]

It is suitable for a very small change or when a specific initial point is used.

2Point elasticity or geometric method

At a point on a straight-line demand curve:

[

E_d=\frac{\text{lower segment of demand curve}}

{\text{upper segment of demand curve}}

]

At the midpoint (E_d=1); above it (E_d>1); below it (E_d<1).

3Arc elasticity

Used for a finite movement between two points:

[

E_d=

\frac{Q_2-Q_1}{P_2-P_1}

\times

\frac{P_1+P_2}{Q_1+Q_2}

]

It avoids getting different answers depending on the direction of movement.

4Total expenditure method

[

TE=P\times Q

]

5Revenue method

For a firm:

[

E_d=\frac{AR}{AR-MR}

]

When (MR>0), demand is elastic; when (MR=0), unit elastic; when (MR<0), inelastic.

Mnemonic — “P-A-T-R”: Percentage, Arc, Total expenditure, Revenue; add geometric point measurement when a curve is supplied.

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Q1(d) Equilibrium price and effects of demand/supply changes

Market equilibrium occurs where quantity demanded equals quantity supplied:

[

Q_d=Q_s

]

At the intersection of (D) and (S), equilibrium price (P_e) and equilibrium quantity (Q_e) are determined.

Adjustment mechanism

Comparative statics

Simultaneous shifts

Diagram strategy: Draw four small panels for the four single shifts. Label initial equilibrium (E), new equilibrium (E_1), and dotted price/quantity projections.

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Q2: Consumer Behaviour

Q2(a) Why an indifference curve may not be convex

The usual indifference curve is convex to the origin because the marginal rate of substitution (MRS) diminishes as the consumer substitutes (X) for (Y). It may fail to be convex when this behavioural assumption does not hold.

Meaning of MRS

[

MRS_{xy}=\left|\frac{\Delta Y}{\Delta X}\right|=\frac{MU_x}{MU_y}

]

Important non-convex cases

Examples and diagram notes

1. Perfect substitutes: Two brands of identical bottled water. The consumer is willing to replace one at a constant rate. Draw parallel straight-line ICs.

2. Perfect complements: Left and right shoes. Extra left shoes alone add no utility. Draw L-shaped ICs with kinks on a ray through the origin.

3. Concave IC: A consumer strongly prefers only tea or only coffee rather than a mixture. MRS rises as (X) replaces (Y). A tangency with a budget line may be a utility minimum; equilibrium tends to occur at a corner.

4. Bad: Pollution and income. More pollution must be compensated with more income; draw upward-sloping ICs.

Important correction to the wording: Indifference curves are normally convex, but they are not necessarily convex in the special preference structures above.

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Q2(b) Budget lines: food and clothing

Let food be (F) on the horizontal axis and clothing be (C) on the vertical axis.

[

P_FF+P_CC=M

]

Given (P_F=₹150) and (P_C=₹300):

[

150F+300C=M

]

Case 1: income ₹6,000

[

F\text{-intercept}=\frac{6000}{150}=40

]

[

C\text{-intercept}=\frac{6000}{300}=20

]

[

C=20-\frac{1}{2}F

]

Slope:

[

-\frac{P_F}{P_C}=-\frac{150}{300}=-0.5

]

Case 2: income changes

Diagram and interpretation

Draw three parallel budget lines. An increase in income shifts the budget line outward because the consumer can buy more of both goods. A fall in income shifts it inward. Since relative prices do not change, the slope remains (-0.5).

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Q2(c) Engel curves from the ICC

An income consumption curve (ICC) joins consumer-equilibrium points as income changes while prices and preferences remain constant. An Engel curve shows the relationship between income and quantity demanded of one good.

Necessary good

• Quantity demanded rises with income, but less than proportionately.

• Income elasticity lies between zero and one.

• Engel curve slopes upward and becomes steeper when income is on the vertical axis.

Luxury good

• Quantity demanded rises more than proportionately with income.

• Income elasticity is greater than one.

• Engel curve slopes upward and becomes relatively flatter when income is vertical.

Inferior good

• Demand initially may rise, but beyond a threshold it falls as income rises.

• Income elasticity is negative in the inferior range.

• ICC bends backward toward the axis of the inferior good; the Engel curve bends backward.

Diagram requirement: Use two panels for each good—ICC in commodity space, then the corresponding Engel curve with income on the vertical axis.

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Q2(d) Substitution and income effects of a price change: normal good

For a normal good (X), a fall in (P_x) rotates the budget line outward along the (X)-axis. The total increase in (X) consists of:

[

\text{Price effect}=\text{Substitution effect}+\text{Income effect}

]

Hicksian decomposition

1. Initial budget line (AB) is tangent to (IC_1) at (E_1).

2. A fall in (P_x) rotates it to (AB_1); final equilibrium is (E_3) on (IC_2).

3. Draw a hypothetical compensated line parallel to (AB_1) and tangent to (IC_1) at (E_2).

4. (E_1\to E_2) is the substitution effect: (X) becomes relatively cheaper, so more (X) is purchased.

5. (E_2\to E_3) is the income effect: purchasing power rises, and because (X) is normal, more (X) is purchased.

Memory line: For a normal good after a price fall, both arrows point toward more (X).

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Q3: Production and Cost

Q3(a) Stages of production and rational stage

The law of variable proportions studies output when one input is variable and at least one input is fixed.

[

AP_L=\frac{TP}{L}, \qquad MP_L=\frac{\Delta TP}{\Delta L}

]

Three stages

Why Stage II is rational

• A producer will not stop in Stage I because the fixed factor is underutilized and adding the variable factor raises its efficiency.

• A producer will not operate in Stage III because marginal product is negative; reducing the variable input would increase output and lower cost.

• Therefore, the rational producer operates in Stage II, where MP is positive but diminishing.

• The exact equilibrium inside Stage II depends on input and output prices:

[

VMP_L=MP_L\times P_Q=P_L

]

Reasons behind the law

Indivisibility of fixed factors and specialization cause early increasing returns; later, the fixed input becomes a constraint, coordination worsens and diminishing/negative returns arise.

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Q3(b) Long-run average and marginal cost curves

In the long run all inputs are variable. The firm can choose plant size.

[

LAC=\frac{LTC}{Q}, \qquad LMC=\frac{\Delta LTC}{\Delta Q}

]

LAC curve

Traditional LAC is U-shaped:

• It falls because of economies of scale.

• It reaches a minimum at the optimum scale.

• It rises because of diseconomies of scale.

• It is the lower envelope of a family of SAC curves and is called the planning curve.

LMC curve

LMC shows the addition to long-run total cost from one more unit of output.

Why LAC is an envelope but LMC is not

LAC is tangent to the relevant SAC for the least-cost plant at each output. LMC is derived from changes in LTC and generally intersects the relevant SMC curves rather than remaining tangent to them.

Modern view

Empirical LAC may be L-shaped or saucer-shaped: costs fall initially and then remain nearly constant because firms can replicate efficient plants, use flexible technology and retain managerial specialization.

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Q3(c) MRTS and least-cost input combination

The marginal rate of technical substitution of labour for capital is the amount of capital that can be reduced when one extra unit of labour is employed while output remains constant:

[

MRTS_{LK}=\left|-\frac{\Delta K}{\Delta L}\right|

=\frac{MP_L}{MP_K}

]

Least-cost condition

[

\frac{MP_L}{P_L}=\frac{MP_K}{P_K}

]

or

[

MRTS_{LK}=\frac{P_L}{P_K}

]

[

MP_K=5,\quad MP_L=10,\quad P_K=2,\quad P_L=6

]

Marginal product per rupee:

[

\frac{MP_K}{P_K}=\frac{5}{2}=2.5

]

[

\frac{MP_L}{P_L}=\frac{10}{6}=1.667

]

Since (2.5\ne1.667), the firm is not using the least-cost combination. Capital produces more output per rupee.

Cross-check:

[

MRTS_{LK}=\frac{10}{5}=2,\qquad

\frac{P_L}{P_K}=\frac{6}{2}=3

]

Again, the tangency condition fails.

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Q3(d) Isoquants, properties and producer equilibrium

An isoquant is the locus of combinations of two inputs that produce the same output:

[

Q=f(L,K)=\bar Q

]

Properties

Possible shapes

Isocost line

[

C=P_LL+P_KK

]

Slope:

[

-\frac{P_L}{P_K}

]

1. Cost minimization for a given output

Choose the lowest isocost line that touches the required isoquant:

[

MRTS_{LK}=\frac{P_L}{P_K}

]

and the isoquant must be convex at the tangency.

2. Output maximization for a given cost

Choose the highest attainable isoquant tangent to the fixed isocost line. The same tangency condition applies.

Corner solution

If tangency is impossible, the least-cost or maximum-output solution may be at an axis/corner, especially with perfect-substitute inputs. Therefore tangency is sufficient only with appropriate convexity and an interior solution.

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Q4: Market Structures

Q4(a) Perfect competition: short-run, long-run and shutdown

Assumptions

Many buyers and sellers, homogeneous product, free entry and exit, perfect knowledge, factor mobility and price-taking behaviour.

For a competitive firm:

[

P=AR=MR

]

Marginal principle

Profit is maximized where:

[

MR=MC

]

and MC cuts MR from below.

Short-run cases

Shutdown point

The shutdown point is the minimum point of AVC:

[

P=MC=\min AVC

]

At this price, total revenue exactly covers total variable cost. Below it, producing adds more to loss than closing temporarily. Fixed cost must be paid in either case.

Long-run equilibrium

Entry occurs when firms earn supernormal profit; exit occurs when they suffer loss. Adjustment ends when:

[

P=MR=LMC=LAC_{\min}

]

The firm earns normal profit and operates at optimum plant size. Long-run equilibrium delivers productive efficiency ((P=\min LAC)) and allocative efficiency ((P=MC)).

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Q4(b) Monopolistic competition versus monopoly; equilibrium

Difference table

Short-run equilibrium under monopolistic competition

The firm chooses output where:

[

MR=SMC

]

with SMC cutting MR from below. Price is read from the downward-sloping AR/demand curve. It may earn supernormal profit, normal profit or loss depending on the position of SAC.

Long-run equilibrium

Supernormal profit attracts entry. New differentiated products reduce each existing firm’s demand and make it more elastic. Loss causes exit. Equilibrium occurs when:

[

MR=LMC

]

and

[

AR=LAC

]

The demand curve is tangent to LAC, usually to the left of minimum LAC.

Excess capacity

Long-run output is below the output that minimizes LAC:

[

\text{Excess capacity}=Q_{\min LAC}-Q_{\text{actual}}

]

It is the cost of product variety and downward-sloping demand, though it may also give firms flexibility for demand growth.

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Q4(c) Monopoly equilibrium in short run and long run

The phrase “Monopoly competition market” is treated here as monopoly, because Q4(b) separately covers monopolistic competition.

Monopoly features

One seller, no close substitutes, high barriers to entry and price-making power. The firm’s AR is the market demand curve; MR lies below AR.

Equilibrium rule

[

MR=MC

]

with MC cutting MR from below. Output is determined at the MR–MC intersection; price is then read from the AR curve.

Short-run outcomes

Long-run equilibrium

[

MR=LMC

]

The monopolist selects an appropriate plant and produces where marginal revenue equals long-run marginal cost. Unlike perfect competition:

• entry does not eliminate profit;

• price generally exceeds marginal cost;

• the firm need not produce at minimum LAC;

• supernormal profit can persist because of barriers.

No unique supply curve: The monopolist has no independent supply curve because quantity depends jointly on demand and cost; the same quantity may be supplied at different prices under different demand conditions.

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Q4(d) Degrees of price discrimination and profitability

Price discrimination means selling the same product, not justified by cost differences, at different prices to different buyers or markets.

Conditions

• The firm has market power.

• Markets/buyers can be separated.

• Resale from low-price to high-price market is prevented.

• Elasticities or reservation prices differ.

• Additional revenue exceeds segmentation and enforcement costs.

Degrees

Profitability

First degree

Profitable when reservation prices can be estimated individually and personalization/enforcement costs are low. Output expands until:

[

P_{\text{marginal unit}}=MC

]

Second degree

Profitable when buyers differ in willingness to pay but cannot be identified cheaply. A menu induces self-selection. The menu must satisfy incentive-compatibility and participation conditions.

Third degree

Allocate output so:

[

MR_1=MR_2=\cdots=MC

]

Charge a higher price in the market with less elastic demand:

[

\frac{P-MC}{P}=\frac{1}{|E_d|}

]

Welfare: First-degree discrimination can raise output to the competitive level but transfers surplus to the monopolist. Third-degree discrimination has an ambiguous welfare effect; it is more defensible when it expands total output or serves a market that would otherwise be excluded.

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Q5: Oligopoly and Applied Pricing

Q5(a) Cournot reaction curves and equilibrium

Cournot’s duopoly model assumes two firms produce a homogeneous product, choose quantities simultaneously, have identical or known costs and treat the rival’s output as given.

Let market inverse demand be:

[

P=a-b(q_1+q_2)

]

With zero marginal cost, Firm 1 maximizes:

[

\pi_1=[a-b(q_1+q_2)]q_1

]

Its reaction function is:

[

q_1=\frac{a-bq_2}{2b}

]

Similarly:

[

q_2=\frac{a-bq_1}{2b}

]

Solving the two symmetric reaction functions:

[

q_1=q_2=\frac{a}{3b},\qquad Q=\frac{2a}{3b}

]

Each reaction curve shows the firm’s best output for every possible rival output. Their intersection is stable because neither firm can raise profit by changing its own quantity alone. It is therefore a Nash equilibrium.

Diagram

Put (q_1) on the horizontal axis and (q_2) on the vertical axis. Draw downward-sloping reaction curves (R_1) and (R_2). Their intersection (E) determines the equilibrium pair.

Comparison

Cournot total output is greater than monopoly output but less than perfectly competitive output; its price lies between monopoly and competitive prices.

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Q5(b)(1) Peak-load pricing

Peak-load pricing means charging a higher price during periods of high demand and a lower price during off-peak periods, especially where capacity is fixed in the short run and output cannot be stored cheaply.

Logic

Applications include electricity, airlines, hotels, ride-hailing, telecom and toll roads.

Managerial benefits: demand smoothing, reduced congestion, better capacity utilization, recovery of capacity cost and improved investment signals.

Limitations: requires metering/time segmentation, may burden consumers who cannot shift usage, and can appear unfair if pricing rules are opaque.

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Q5(b)(2) Rent control in the short run and long run

Rent control is a legal maximum rent. It is effective when set below the equilibrium rent.

Short run

• Housing supply is highly inelastic because the stock is fixed.

• Quantity demanded rises while quantity supplied changes little.

• A shortage (Q_d-Q_s) arises.

• Existing tenants gain if they retain a controlled unit.

• Non-price rationing, queues, search costs and side payments may appear.

Long run

• Landlords reduce maintenance or convert property to other uses.

• New construction falls.

• Supply becomes more elastic and contracts further.

• The shortage becomes larger; quality deteriorates and labour mobility may fall.

Balanced evaluation: Targeted rent support, housing vouchers or construction subsidies can protect vulnerable tenants with fewer supply distortions, though policy design and fiscal cost matter.

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Q5(c) Prisoner’s dilemma in oligopoly

Oligopolists face a prisoner’s dilemma because collective profit is highest when firms cooperate, but each firm has an individual incentive to cut price, advertise aggressively or expand output. If all defect, every firm may be worse off.

Example payoff matrix

For each firm, cutting price gives a higher payoff regardless of the rival’s action. “Cut price” is the dominant strategy. The Nash equilibrium is ((5,5)), although joint cooperation ((10,10)) is better for both.

Why collusion is difficult

• Secret price cuts are tempting.

• Firms differ in cost, market share and demand.

• Demand conditions change.

• New entry destabilizes agreements.

• Competition law prohibits explicit cartels.

Repeated games

Cooperation may be sustained when interaction is repeated, future profit matters, cheating is observable and credible punishment exists. Even then, legal restrictions on collusion remain.

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Q5(d)(1) Excess-capacity hypothesis

Excess capacity is the gap between the output that minimizes LAC and the smaller output produced by a monopolistically competitive firm in long-run equilibrium:

[

\text{Excess capacity}=Q_{\min LAC}-Q_{LR}

]

Cause-and-effect map

Implications

Chamberlin linked excess capacity with product differentiation and free entry. It is not literally idle machinery in every case; it is mainly output below minimum-LAC scale.

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Q5(d)(2) Kinked demand curve

The kinked-demand model explains price rigidity in oligopoly.

Assumptions about rivals

• If one firm raises price, rivals do not follow; many customers are lost. Demand above the current price is highly elastic.

• If one firm cuts price, rivals match the cut; few customers are gained. Demand below the current price is relatively inelastic.

The demand curve has a kink at current price (P^*). The associated MR curve has a discontinuous vertical gap. If MC shifts within this gap, the profit-maximizing output and price remain unchanged.

Merits and limitations

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