Business Economics — B.Com Sem V (Paper 873, 2024)

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Q1

(a) Demand Definition & Demand Schedule [9]

Demand = a consumer's desire for a commodity, backed by (i) willingness to pay and (ii) ability (purchasing power/resources) to acquire a given quantity, at a particular price, time and place. Mere wish ≠ demand; it must be effective.

Demand Schedule types:

• Individual demand schedule — one consumer's Qd at various prices
• Market demand schedule — horizontal sum of all individual schedules at each price

(b) Cross Elasticity — Pen & Ink (Complementary Goods) [9]

Since Ink's own price is unchanged, the meaningful cross-elasticity is Ink's demand response to Pen's price change: $E_{c} = \frac{\%\Delta Q_{ink}}{\%\Delta P_{pen}} = \frac{(2-4)/4}{(20-10)/10} = \frac{-50\%}{100\%} = \boxed{-0.5}$

Negative cross elasticity ⟹ Pen and Ink are complementary goods — a rise in pen's price (which also reduces pen purchases) drags ink demand down too, since they're consumed together. Diagrammatically, this shows as a leftward shift of Ink's demand curve when Pen's price rises.

(c) Price Elasticity — Total Expenditure Method [9]

$\boxed{A: E_d=1\text{ (Unit elastic)} \qquad B: E_d<1\text{ (Inelastic)} \qquad C: E_d>1\text{ (Elastic)}}$ Rule: if total expenditure stays constant as price changes → unit elastic; if expenditure moves in the same direction as price → inelastic; if it moves opposite to price → elastic.

(d) Equilibrium — Price & Quantity Determination [9]

Equilibrium: point where Demand curve (downward) intersects Supply curve (upward) — Qd = Qs.

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Q2

(a) Why Indifference Curves Are Not Convex (i.e., They're Concave to Origin — Not Convex-to-Origin-Violating) [9]

(Standard theory point: IC is convex to the origin, not "convex" in the everyday sense of bulging outward from origin.) This reflects the diminishing Marginal Rate of Substitution (MRS) — as a consumer gets more of good X, they're willing to give up progressively less of Y to get each additional unit of X (goods are imperfect substitutes, satiation sets in). If ICs were concave to the origin instead, MRS would increase, implying the consumer values extra units of an already-abundant good more — economically irrational for ordinary goods.

(b) Budget Lines — Two Scenarios [9]

Income=₹6,000; Price(Food)=150, Price(Clothing)=300. $\text{Intercepts: Food-axis} = 6000/150=40 \text{ units} \qquad \text{Clothing-axis} = 6000/300=20\text{ units}$ $\text{Slope} = -P_{food}/P_{clothing} = -150/300 = -0.5$

If income → ₹9,000: Budget line shifts outward, parallel (intercepts 60 and 30) — same slope (relative prices unchanged), just more purchasing power. If income → ₹4,500: Budget line shifts inward, parallel (intercepts 30 and 15).

(c) Engel Curves — Necessity, Luxury, Inferior Goods [9]

Derived by plotting quantity demanded against income (from Income-Consumption Curve), holding prices constant:

• Necessity good: Engel curve rises but at a decreasing rate (positive slope, concave) — demand grows slower than income (Engel's Law)
• Luxury good: Engel curve rises at an increasing rate (convex) — demand grows faster than income
• Inferior good: Engel curve is positively sloped initially, then bends backward (negative slope) beyond a threshold income — demand falls as income keeps rising (consumer switches to superior substitutes)

(d) Income & Substitution Effects — Price Fall, Normal Good [9]

Starting at consumer equilibrium $E_1$ (IC₁ tangent to original budget line):

1. Price of X falls → budget line rotates outward (pivots on Y-intercept)
2. Substitution Effect: draw a compensated budget line (parallel to new BL, tangent to original IC₁) — movement along IC₁ to new tangency = pure substitution effect (X↑, always positive for normal & inferior goods)
3. Income Effect: shift from the compensated line to the actual new budget line (tangent to IC₂) — for a normal good, income effect reinforces substitution effect (X↑ further)
4. Total Price Effect = Substitution Effect + Income Effect, both positive for a normal good ⟹ demand curve slopes downward.

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Q3

(a) Stages of Production [9]

Rational producer operates in Stage II — it's the only region where both AP and MP are positive but declining, i.e., marginal returns are diminishing yet still productive; adding more of the variable factor beyond this (Stage III) actively reduces output.

(b) Long-Run Average & Marginal Cost Curves [9]

• LAC is U-shaped (though flatter than SAC) — falls due to economies of scale, rises due to diseconomies of scale
• LMC cuts LAC at LAC's minimum point
• LMC lies below LAC while LAC falls, above LAC while LAC rises — standard average-marginal relationship

OR (c) MRTS & Optimal Input Combination [9]

$MRTS_{LK} = \frac{MP_L}{MP_K} = \frac{10}{5}=2$

Least-cost condition: $\dfrac{MP_L}{P_L} = \dfrac{MP_K}{P_K}$ $\frac{MP_L}{P_L}=\frac{10}{6}=1.667 \qquad \frac{MP_K}{P_K}=\frac{5}{2}=2.5$

Since $1.667 \ne 2.5$, the firm is NOT at the minimum-cost input combination.

$\boxed{\text{Since } MP_K/P_K > MP_L/P_L\text{, capital gives more output per rupee — the firm should use MORE K and LESS L}}$ until the two ratios equalize (moving along the isoquant toward the tangency with an isocost line).

(d) Isoquants & Producer's Equilibrium [9]

Isoquant: curve showing all combinations of two inputs (K, L) yielding the same level of output. Features: downward-sloping, convex to origin (diminishing MRTS), higher isoquants = higher output, non-intersecting.

• (i) Cost minimization for given output: producer picks the point where the isoquant is tangent to the lowest possible isocost line — $MRTS_{LK} = P_L/P_K$
• (ii) Output maximization for given cost: producer picks the point where the isocost line is tangent to the highest attainable isoquant — same tangency condition, viewed from the opposite constraint

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Q4

(a) Shut-Down Point — Perfect Competition [9]

Shut-down point: where Price = minimum of Average Variable Cost (AVC). Below this price, the firm can't even cover variable costs, so it minimizes losses by shutting down (loss = only fixed costs) rather than producing (loss = fixed costs + uncovered variable costs).

• If $AVC_{min} < P < AC_{min}$: firm continues to operate short-run despite loss (covers all VC + part of FC)
• If $P < AVC_{min}$: firm shuts down immediately

(b) Indeterminate Supply Curve Under Monopoly [9]

Under perfect competition, supply curve = the portion of MC above AVC (a unique P→Q mapping) because P=MC at equilibrium. Under monopoly, the firm sets output where MR=MC, not P=MC — and MR depends on the shape of the demand curve the monopolist faces, which can differ for the same price across situations. So the same price can be associated with different quantities (depending on demand elasticity/shape at that point) — there's no unique, price-independent supply schedule. Hence "monopoly has no supply curve."

OR (c) Monopolistic Competition — Equilibrium [9]

• Short-run: firms can earn abnormal profit or loss (like monopoly, since products are differentiated) — equilibrium at MR=MC
• Long-run: free entry/exit erodes abnormal profits — new entrants attracted by profits shift the firm's demand curve left until Price = Average Cost (zero economic profit), but unlike perfect competition, this happens at output below the minimum-AC point (tangency solution) — leaving excess capacity.

(d) Oligopoly — Features & Price Rigidity [9]

Features: few sellers, mutual interdependence, entry barriers, non-price competition common, indeterminate demand curve (depends on rivals' reactions).

Price rigidity (Kinked Demand Curve): each firm believes rivals will match a price cut (to avoid losing customers) but won't follow a price rise (happy to gain customers) — this creates a demand curve kinked at the current price: relatively elastic above, inelastic below. The kink produces a discontinuous MR curve, so moderate shifts in MC pass through the gap without changing the profit-maximizing price — hence price stays "sticky/rigid" even as costs fluctuate.

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Q5

(a) Cournot's Duopoly & Reaction Curves [9]

Each duopolist sets output assuming the rival's current output stays fixed, then reacts optimally — the reaction curve of firm 1 shows its profit-maximizing output for every possible output of firm 2 (and vice-versa). Cournot's equilibrium is where the two reaction curves intersect — the only point where both firms' output choices are simultaneously optimal given what the other is doing (a Nash equilibrium in output).

(b) Short Notes [9]

• Peak Load Pricing: charging a higher price during high-demand ("peak") periods and lower price off-peak — used where capacity is fixed/costly to expand (electricity, telecom, transport) to ration scarce capacity and smooth demand.
• Rent Control:
  • Short-run: imposing a ceiling below equilibrium rent creates a shortage (Qd > Qs), but since housing supply is near-fixed short-run, minimal supply reduction — mainly a transfer from landlords to (lucky) tenants.
  • Long-run: landlords under-maintain/exit the rental market, supply of rental housing shrinks further — the shortage worsens over time as supply is more elastic long-run.

OR (c) Oligopoly & Prisoners' Dilemma [9]

Oligopolists face a prisoners' dilemma because each firm's individually rational choice (e.g., cut price/cheat on a cartel agreement) leads to a collectively worse outcome (price war, lower industry profits) than if all cooperated — yet no firm can trust others not to cheat, so the non-cooperative (defect-defect) outcome is the stable Nash equilibrium.

(d) Short Notes [9]

• Excess Capacity Hypothesis (Monopolistic Competition): in long-run equilibrium, firms produce at an output less than the output that minimizes average cost, because the tangency of the (downward-sloping) demand curve with AC occurs left of AC's minimum — this "unused" capacity is the cost of product differentiation/variety to consumers.
• Kinked Demand Curve: (see Q4(d) above) — explains oligopoly price rigidity via asymmetric reactions to price rises vs cuts.

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