Intermediate Microeconomics (often coded as ECON2000 at South African universities) builds the analytical tools you need to understand how individuals, firms, and markets respond to incentives. These notes focus on the core microeconomic “engines” behind pricing, consumer choice, firm behaviour, market structure, and policy—especially where the analysis becomes exam-relevant: deriving demand and supply, interpreting equilibrium, comparing outcomes across market models, and reasoning about welfare. The goal is to help you move from definitions to graphs, from graphs to algebra, and from algebra to clear conclusions.
Section 1: Foundations—Methods, Demand, and Consumer Choice (ECON2000 Core Toolkit)
1.1 The microeconomic mindset: optimisation under constraints
Most ECON2000 problems reduce to the same pattern:
- Identify agents (consumer or firm).
- Specify preferences/technology (utility function or production function).
- Write constraints (budget constraint, time constraint, resource constraints).
- Optimise (choose quantities to maximise utility or minimise cost, etc.).
- Interpret the solution (comparative statics, elasticities, welfare implications).
A key exam skill is moving between three representations:
- Word description (e.g., “diminishing marginal utility”)
- Graph (e.g., indifference curves and budget line)
- Math (e.g., Lagrangian first-order conditions)
Example: budget constraint in a two-good economy
Let a consumer consume x (bread) and y (milk). Income is m, prices are pₓ and pᵧ.
The budget constraint is:
[
p_x x + p_y y \le m
]
At an interior optimum:
[
p_x x + p_y y = m
]
1.2 Preferences and indifference curves
Preferences are typically assumed to satisfy:
- Completeness (can compare any two bundles)
- Transitivity (consistent ranking)
- Continuity
- Often local non-satiation (more is better, at least locally)
Diminishing marginal rate of substitution (MRS)
Indifference curves are usually drawn convex to the origin. Convexity corresponds to diminishing MRS:
[
\text{MRS}_{xy} ; \text{decreases as} ; x ; \text{increases (along an IC)}
]
This connects directly to “standard” utility assumptions like quasi-concavity.
1.3 Utility maximisation via the Lagrangian
A common setup:
[
\max_{x,y} ; U(x,y) \quad \text{s.t.}\quad p_x x + p_y y = m
]
Lagrangian:
[
\mathcal{L} = U(x,y) + \lambda (m – p_x x – p_y y)
]
First-order conditions:
[
\frac{\partial U}{\partial x} = \lambda p_x,\quad \frac{\partial U}{\partial y} = \lambda p_y
]
Divide to eliminate λ:
[
\frac{\partial U/\partial x}{\partial U/\partial y} = \frac{p_x}{p_y}
]
But the left-hand side is the MRS:
[
\text{MRS}_{xy} = \frac{p_x}{p_y}
]
Exam interpretation: at the optimum, the consumer’s willingness to trade off y for x equals the market’s opportunity cost ratio.
1.4 Consumer demand: Hicksian vs Marshallian intuition
ECON2000 exams often distinguish between:
- Marshallian (ordinary) demand: depends on prices and income ((x(p_x,p_y,m))).
- Hicksian (compensated) demand: depends on prices and a utility target ((x(p_x,p_y,\bar{U}))).
Even if you are not asked to derive Hicksian demand fully, you must understand the idea behind income vs substitution effects.
1.5 Income and substitution effects: normal vs inferior goods
When the price of good (x) changes, the total effect on demand can be decomposed:
- Substitution effect: consumer substitutes away from the relatively more expensive good.
- Income effect: the consumer’s real purchasing power changes.
Normal good
If (x) is normal, higher income raises demand; thus when the price of (x) rises, income effect goes in the direction of lower demand, reinforcing substitution.
Inferior good
If (x) is inferior, higher income lowers demand; therefore when price of (x) rises (and real income falls), demand may increase—potentially producing a Giffen good scenario (rare and requires strong conditions).
1.6 Revealed preference and demand curve logic
Many syllabi include the idea that demand behaviour is consistent with preferences under certain axioms. While full revealed preference theory may not be required, you should be able to reason with:
- Law of demand: higher price → lower quantity demanded (typically).
- Shifts: changes in tastes, income, expectations, substitutes/complements.
- Movements along the curve: price change only.
1.7 From utility to elasticity: key definitions
Elasticity is crucial for interpreting policy and market response.
Price elasticity of demand
[
\epsilon_{x,p_x} = \frac{\partial x}{\partial p_x}\cdot \frac{p_x}{x}
]
- If (|\epsilon|>1): demand is elastic
- If (|\epsilon|<1): demand is inelastic
- If (\epsilon=-1): unit elasticity (revenue constant when price changes)
Income elasticity
[
\epsilon_{x,m} = \frac{\partial x}{\partial m}\cdot \frac{m}{x}
]
-
0 normal good
- <0 inferior good
1.8 Graph-to-algebra bridge: a worked case
Suppose the demand is:
[
x = a – b p_x + c m
]
Then:
- Demand is downward sloping in price if (b>0).
- Income shifts demand upward if (c>0).
If you’re asked about welfare effects (tax, subsidy), you often need:
- Consumer surplus (CS) and producer surplus (PS)
- Deadweight loss (DWL)
- Tax incidence (who bears the burden)
But you cannot compute those reliably without demand and supply curves.
1.9 South African exam relevance: interpreting “real-world” demand
In South African contexts, exam questions sometimes use examples like:
- food categories,
- transport (public transport vs private transport),
- electricity usage and prepaid tariffs,
- student living costs.
The key micro message is the same: prices matter, and elasticities determine how strongly consumers respond.
Example scenario (typical):
A commuter changes from an expensive private ride to a cheaper minibus taxi when fuel prices increase. In micro terms, private transport is relatively price-sensitive if substitutes exist and the time horizon is long enough to switch.
Section 2: Production, Costs, and Firm Behaviour—From Technology to Supply
2.1 Production functions and marginal products
Firms combine inputs to produce output. A production function:
[
q = f(L,K)
]
where L is labour and K is capital.
Key concepts:
- Total product: output at different input levels
- Marginal product (MP): extra output from one additional input
[
MP_L = \frac{\partial f}{\partial L}
] - Diminishing marginal returns: after some point, MP falls (holding other input fixed)
In graphs and exam problems, diminishing returns imply increasing marginal cost eventually.
2.2 Returns to scale vs diminishing returns
- Returns to scale: what happens when you scale both inputs up by a factor.
- Increasing returns: output more than proportional
- Constant returns: output proportional
- Decreasing returns: output less than proportional
- Diminishing marginal returns: what happens when you scale one input while holding others fixed.
These are different. Many students confuse them.
Quick exam test
- If doubling L and K doubles output: constant returns to scale
- If doubling L while K fixed eventually leads to MP falling: diminishing returns (in that fixed-K context)
2.3 Cost curves: linking production to costs
Assume input prices:
- wage (w) for labour
- rental rate (r) for capital
Then:
[
C = wL + rK
]
The firm chooses inputs to minimise cost for a target output level (q). You get:
- Average cost (AC = \frac{C}{q})
- Marginal cost (MC = \frac{dC}{dq}) (or discrete approximation)
Typical shape logic
- (MC) initially falls then rises
- (AC) often has a U-shape with (MC) cutting (AC) at its minimum
Exam rule of thumb: where (MC<AC), average cost decreases; where (MC>AC), average cost increases.
2.4 Cost structures: fixed vs variable cost
If a firm has fixed cost (F) (short-run) and variable cost (VC(q)), then:
[
C(q)=F+VC(q)
]
In the short run:
- (F) does not change with output
- (VC) changes with output
So:
[
AC=\frac{F}{q}+\frac{VC(q)}{q}
]
As (q) rises, (\frac{F}{q}) falls.
2.5 Short-run firm decision: maximise profit
Profit:
[
\pi(q)=p\cdot q – C(q)
]
If the firm is a price taker in a competitive market:
- Choose (q) where:
[
p=MC(q)
]
provided it produces.
But whether to produce depends on shutdown conditions:
- Produce if:
[
p \ge AVC \quad (\text{average variable cost})
] - Shutdown if:
[
p < AVC
]
In shutdown, the firm incurs only fixed cost (F), not variable costs.
Why AVC?
Because if the firm can’t cover variable costs, producing increases losses compared to shutting down.
2.6 Firm supply in competitive markets
In perfect competition, the firm’s supply curve in the short run corresponds to the part of the MC curve above AVC.
That logic is frequently tested with:
- “Explain why supply equals MC above AVC”
- “Graph and interpret a price change” question
2.7 Long-run adjustment and free entry
In the long run, firms can enter or exit. In a zero-profit equilibrium:
[
\pi = 0 \Rightarrow p = AC(q)
]
If profit is positive:
- entry occurs
- supply increases
- price falls
until profits are driven to zero.
If profit is negative:
- exit occurs
- supply decreases
- price rises
until again profits are driven to zero.
2.8 Worked numerical illustration: cost curves and output choice
Suppose a competitive firm has:
- Total cost (C(q)= 20 + 5q + q^2)
- Market price (p) varies
Compute:
[
\pi(q)=pq – (20+5q+q^2)
]
Marginal cost:
[
MC(q)=\frac{dC}{dq}=5+2q
]
Set (p=MC):
[
p=5+2q \Rightarrow q=\frac{p-5}{2}
]
- Shutdown requires (p \ge AVC).
Compute (VC(q)=5q+q^2).
[
AVC(q)=\frac{5q+q^2}{q}=5+q
]
Condition (p \ge 5+q). Substitute (q=\frac{p-5}{2}):
[
p \ge 5+\frac{p-5}{2}
\Rightarrow 2p \ge 10 + p – 5
\Rightarrow 2p \ge p + 5
\Rightarrow p \ge 5
]
So shutdown occurs if (p<5). This matches intuition: if price is below the intercept-like level of costs, producing is not worthwhile.
2.9 Market-level supply aggregation
If there are multiple firms, market supply is the horizontal sum of individual supplies.
Exam tip: if you only derive firm output as a function of price (q_i(p)), you must then:
- sum across (i) to get (Q(p))
- invert (Q(p)) into (p(Q)) if needed for consumer surplus calculations.
2.10 South Africa context: cost and technology constraints
South African microeconomic problems often use realistic constraints:
- energy costs (electricity tariffs)
- labour costs and wage bargaining
- infrastructure and logistics costs
Even when the numbers change, the core micro principle remains:
- Firms have fixed constraints in the short run
- They adapt in the long run by changing capital, technology, and scale
- Market prices determine output where marginal benefit equals marginal cost (or where marginal revenue equals marginal cost in non-competitive settings)
Section 3: Market Structures—Perfect Competition, Monopoly, and Strategic Reasoning
3.1 Perfect competition: assumptions and equilibrium
Perfect competition assumes:
- many buyers and sellers
- homogenous product
- firms are price takers
- free entry/exit (in the long run)
In equilibrium (short run), a competitive firm chooses (q) where:
[
p=MC(q)
]
Market equilibrium is where:
[
D(p)=S(p)
]
Welfare analysis:
- In perfect competition (with no externalities and full information), equilibrium is efficient: production occurs at the point where marginal cost equals marginal willingness to pay.
In terms of surpluses:
- Consumer surplus + producer surplus is maximised relative to distortions from taxes and market power.
3.2 Monopoly: market power and downward-sloping demand
A monopoly faces the market demand curve. Unlike competitive firms, it can influence price. Therefore:
- It chooses output to maximise profit considering how price changes with quantity.
Total revenue:
[
TR(q)=p(q)\cdot q
]
Marginal revenue:
[
MR(q)=\frac{dTR}{dq}
]
Monopoly condition:
[
MR(q)=MC(q)
]
Then monopoly sets the price from demand at that quantity.
Key graph relationship
- Demand curve is downward sloping.
- MR lies below demand for a typical downward-sloping demand.
- The “wedge” between demand price and MR reflects how selling more requires reducing price for all units.
3.3 Monopoly output vs competitive output
Compare:
- Competitive equilibrium: (p=MC)
- Monopoly: (MR=MC) with (MR<p) (when demand slopes downward)
Thus:
- Monopoly output is lower
- Monopoly price is higher
Welfare implications:
- Monopoly leads to deadweight loss because some mutually beneficial trades do not occur.
3.4 Numerical monopoly example (exam-style)
Let demand be linear:
[
p(q)=100-2q
]
Then:
[
TR(q)= (100-2q)q = 100q-2q^2
]
[
MR(q)=\frac{dTR}{dq}=100-4q
]
Suppose marginal cost is:
[
MC(q)=20+q
]
Set (MR=MC):
[
100-4q = 20+q
\Rightarrow 80=5q
\Rightarrow q^=16
]
Price:
[
p^=100-2(16)=68
]
If competition prevailed with (p=MC):
[
100-2q = 20+q
\Rightarrow 80=3q
\Rightarrow q_c = 26.\overline{6}
]
Monopoly output is smaller:
- (16) vs (26.67)
and monopoly price is higher: - (68) vs (p=100-2(26.67)\approx 46.67)
This kind of contrast is usually expected when a question asks “compare outputs/prices” across structures.
3.5 Elasticity and the monopoly pricing rule (important)
A classic formula connects monopoly markup to demand elasticity:
[
\frac{p-MC}{p}=\frac{1}{|\epsilon|}
]
where (|\epsilon|) is the absolute value of demand elasticity at the chosen quantity.
Interpretation:
- If demand is inelastic ((|\epsilon|) small), markup is larger.
- If demand is elastic, markup is smaller.
You should be able to use this formula to:
- compute the optimal price given (MC) and elasticity
- explain why monopolies prefer markets with fewer substitutes
3.6 Imperfect competition beyond monopoly: oligopoly intuition
Many ECON2000 syllabi extend to:
- strategic behaviour,
- game theoretic intuition (even if not fully advanced).
Common oligopoly models include:
- Cournot quantity competition
- Bertrand price competition
- collusion and cartel effects
Even when not formally required, exams often ask:
- “What’s the intuition of strategic interdependence?”
- “How do outputs/prices change when firms compete?”
3.7 Cournot model (quantity setting): core logic
Two firms choose quantities (q_1), (q_2). Total quantity:
[
Q=q_1+q_2
]
Market price depends on (Q):
[
p(Q)
]
Firm (i) profit:
[
\pi_i = p(Q)\cdot q_i – C_i(q_i)
]
Each firm chooses (q_i) to maximise (\pi_i) given (q_j).
Best response functions lead to Nash equilibrium where:
- no firm can unilaterally change quantity to improve profit.
Exam intuition:
- When firms compete in quantities, the equilibrium tends to lie between monopoly and perfect competition:
- more competition than monopoly
- less competition than perfect competition (because each firm’s output decision affects price)
3.8 Bertrand model (price setting): core logic
Bertrand competition assumes firms choose prices (p_1), (p_2). If products are identical:
- If one firm charges a lower price, it captures the whole market.
- In equilibrium, under constant marginal cost and identical products, prices often collapse to marginal cost (the “Bertrand paradox”).
Exam question types:
- “Explain why price competition can eliminate markup”
- “Discuss conditions under which Bertrand outcome differs”
3.9 Collusion and cartel incentives
Cartels try to mimic monopoly by coordinating outputs. But collusion is unstable because each firm has an incentive to “cheat”:
- Cheating yields higher short-run profit if others stick to cartel quantities.
- Enforcement mechanisms, repeated games, and punishments determine whether collusion sustains.
In exams, you might be asked:
- “Why is collusion difficult in one-shot games?”
- “How do repeated interactions affect incentives?”
3.10 Policy relevance: regulation, taxes, and welfare
Market power creates a wedge between:
- marginal willingness to pay and marginal cost
leading to inefficiency.
Possible policy tools:
- competition policy (anti-trust)
- price regulation (e.g., for utilities)
- taxation and subsidies (but must consider elasticities and incidence)
A typical welfare statement:
- Taxes create deadweight loss even if revenue is collected.
- Monopoly creates deadweight loss without tax revenue.
3.11 South African application: natural monopoly and network industries
South Africa has industries where network effects and infrastructure costs make them “natural monopolies” (or at least likely candidates):
- electricity generation/transmission/distribution
- water distribution (in many contexts)
- rail and ports (certain segments)
Micro message:
- If high fixed costs mean average cost falls over a wide range, competitive entry may be inefficient.
- But monopoly still creates welfare loss if prices exceed marginal cost.
Hence regulatory models aim to balance: - cost recovery (avoid underinvestment)
- efficiency (avoid persistent price distortions)
- fairness and access (social objectives)
Section 4: General Equilibrium Elements, Market Failures, and Welfare Analysis (Taxes, Externalities, Public Goods)
4.1 Partial vs general equilibrium
A large portion of ECON2000 is partial equilibrium:
- focus on one market
- treat others as fixed
General equilibrium considers:
- interactions across markets
- budget constraints, factor markets, and cross-price effects.
But even in partial equilibrium courses, welfare analysis often implicitly uses general equilibrium ideas through budget constraints and incidence.
4.2 Consumer surplus, producer surplus, and total surplus
In a market with demand (D(p)) and supply (S(p)):
- Consumer surplus: area between demand and price
- Producer surplus: area between price and supply
Total surplus:
[
TS = CS + PS
]
Efficiency in competitive equilibrium corresponds to maximising total surplus (under assumptions: no externalities, no market power, etc.).
4.3 Taxes: incidence, deadweight loss, and elasticities
Let a per-unit tax (t) be imposed on sellers (or buyers; incidence ultimately depends on elasticities).
If demand is inelastic and supply is elastic:
- consumers bear more of the tax burden (price increases modestly? actually sellers reduce output more? Use incidence logic carefully)
The standard qualitative rule: - More elastic side bears less of the burden.
- Less elastic side bears more.
Deadweight loss arises because the tax distorts quantity away from efficient level.
Diagram logic for exam answers
- Without tax: (p^) and (Q^)
- With tax: quantity decreases to (Q_t < Q^*)
- Prices differ:
- buyers pay (p_b)
- sellers receive (p_s = p_b – t)
Surplus loss:
- CS decreases
- PS decreases
- tax revenue collected reduces part of the loss
- remaining loss is DWL
4.4 A numerical tax incidence example
Suppose demand:
[
Q_d = 100 – 2p
]
Supply:
[
Q_s = 10 + p
]
At equilibrium (Q_d=Q_s):
[
100 – 2p = 10 + p \Rightarrow 90 = 3p \Rightarrow p^* = 30
]
Quantity:
[
Q^* = 10 + 30 = 40
]
Impose tax (t=10) per unit on sellers. Sellers receive (p_s = p_b – 10). In supply equation:
[
Q_s = 10 + p_s = 10 + (p_b – 10) = p_b
]
Demand:
[
Q_d = 100 – 2p_b
]
Set equal:
[
100 – 2p_b = p_b \Rightarrow 100=3p_b \Rightarrow p_b = 33.\overline{3}
]
Then:
[
p_s = 23.\overline{3}
]
Quantity with tax:
[
Q_t = p_b = 33.\overline{3}
]
So quantity falls:
[
\Delta Q = 40 – 33.\overline{3} = 6.\overline{6}
]
This is DWL from fewer trades.
If asked for tax revenue:
[
\text{Revenue} = t\cdot Q_t = 10 \cdot 33.\overline{3}=333.\overline{3}
]
You’d then compute CS and PS changes to get DWL.
4.5 Externalities: private vs social marginal costs/benefits
Externalities mean third parties are affected by actions, so private decision-making is not aligned with social efficiency.
- Negative externality (pollution): social marginal cost (SMC) > private marginal cost (PMC)
- Positive externality (education/inoculation): social marginal benefit (SMB) > private marginal benefit (PMB)
Efficient output occurs where:
- negative externality: (SMC = D) (or (MB = SMC))
- positive externality: (SMB = S) (or (MSB = MC))
4.6 Pigouvian taxes/subsidies
To internalise externality:
Negative externality → Pigouvian tax
Tax equals the marginal external damage:
[
t = MEC = SMC – PMC
]
Positive externality → Pigouvian subsidy
Subsidy equals marginal external benefit:
[
s = MEB = SMB – MPB
]
Exam relevance:
- show how tax shifts the supply cost to reflect the external damage
- interpret policy: government forces private marginal cost to align with social marginal cost
4.7 Example: pollution externality (analytical)
Suppose inverse demand:
[
p = 100 – Q
]
Private cost implies marginal private cost:
[
PMC = MC_p(Q)= Q
]
External damage per unit:
[
MD(Q)= 20
]
Then:
[
SMC = PMC + MD = Q + 20
]
Efficient output where price (MB) equals SMC:
[
100 – Q = Q + 20 \Rightarrow 80 = 2Q \Rightarrow Q_{eff} = 40
]
Market output with no externality where price equals PMC:
[
100 – Q = Q \Rightarrow 100=2Q \Rightarrow Q_{mkt}=50
]
Overproduction occurs:
[
50 > 40
]
Pigouvian tax:
[
t = MD = 20
]
This reduces quantity to 40 in a standard setup (depending on functional forms).
4.8 Public goods and the free-rider problem
A public good is non-rival and non-excludable (or hard to exclude). Examples:
- national defence,
- some public broadcasting,
- street lighting,
- basic environmental protection.
The free-rider problem:
- individuals understate their willingness to pay because they enjoy benefits regardless of contributing.
Efficient provision requires:
- total marginal benefit equals marginal cost
- but private marginal benefit reflects only the individual’s part, not the full social benefit.
In exam questions, you may be asked:
- why summing willingness-to-pay differs from private demand,
- how public provision changes equilibrium.
4.9 Common missteps: when you must justify, not just state
Typical marks-lost mistakes:
- claiming “tax reduces consumption” without incidence or elasticity discussion
- saying “externalities always cause market failure” without connecting to divergence of marginal conditions
- providing a welfare conclusion but not linking it to CS/PS or total surplus
Better approach:
- state the relevant marginal condition
- show how market equilibrium violates it
- explain the welfare direction (over/under production)
4.10 South African policy examples (used as micro cases)
South African policy questions often connect to:
- energy subsidies/tariffs,
- public health interventions (vaccination),
- education policies,
- environmental regulation (air quality, water pollution),
- transport pricing.
Even if the course uses simplified models, your analysis should remain micro-consistent:
- determine whether the policy acts like a tax or subsidy,
- identify elasticities relevant to demand/supply response,
- determine whether welfare increases by moving closer to efficient marginal conditions.
Section 5: Advanced Exam Skills—Welfare, Risk, Choice Under Uncertainty, and Problem-Solving Templates
5.1 Welfare change decomposition: compensated demand and equivalent variation intuition
Sometimes ECON2000 asks you to compute or interpret welfare changes from price or policy changes.
Key ideas:
- Equivalent Variation (EV): how much income change makes the consumer as well off under new prices as before.
- Compensating Variation (CV): how much income change makes the consumer as well off under old prices as after.
You may not always compute EV/CV numerically, but you should know:
- why real income changes can be separated from substitution effects,
- that welfare triangles depend on elasticity/functional forms when computing approximate measures.
5.2 Choice under uncertainty: expected utility vs expected value
Intermediate micro often includes decision-making under risk.
Expected value (naive)
[
E[X]=\sum p_i x_i
]
But expected value ignores risk preferences.
Expected utility
Let utility over outcomes be (u(x)). Then:
[
E[u(x)] = \sum p_i u(x_i)
]
A risk-averse individual has:
- concave utility (u''<0),
- prefers certain outcomes with the same expected value.
Risk premium:
- difference between expected value and certainty equivalent.
Exam relevance: distinguish “risk” from “return”.
5.3 Risk, insurance, and actuarially fair premiums
Insurance provides protection against downside risk. A key benchmark:
- actuarially fair premium equals expected payout.
If:
- premium > fair premium → insurance is expensive and less likely to be purchased
- premium = fair → only risk aversion drives demand
- premium < fair (rare) → demand increases strongly
In a typical insurance model:
- Insurance shifts wealth distribution
- The consumer trades premium cost for reduced variance in consumption
5.4 Market insurance and adverse selection: core intuition
If information is asymmetric (insurers can’t observe risk type), then adverse selection may occur:
- high-risk individuals are more willing to buy insurance
- insurers face higher expected payouts
- premiums rise
- low-risk drop out
- leaving a market “unravelling” outcome.
Even if you don’t do full formal models, you should articulate:
- how private information affects market outcomes,
- why equilibrium differs from symmetric-information benchmark.
5.5 Consumer choice with intertemporal budget constraints (if covered)
Some intermediate micro syllabi include basic intertemporal choice:
- consumers choose consumption today (c_1) and tomorrow (c_2)
- subject to present value of income.
A common constraint:
[
c_1 + \frac{c_2}{1+r} = m
]
where (r) is the interest rate.
Key exam logic:
- higher (r) changes relative price of future consumption
- substitution effect depends on whether consumption responses follow normality of intertemporal substitution
- income effect depends on endowment structure
5.6 Quantitative welfare with tax and externalities: standard triangles and wedges
When compute deadweight loss, remember:
- DWL arises from reduced quantity relative to efficient benchmark.
- Under linear demand and supply, DWL is often proportional to:
- square of tax wedge
- or area of triangles based on shifts.
A robust method:
- compute pre-policy equilibrium (Q^), (p^).
- compute post-policy equilibrium (Q_t), (p_b), (p_s).
- compute CS and PS changes using triangle/trapezoid geometry.
- DWL = loss in total surplus = (CS loss + PS loss − tax revenue change if tax exists).
If you can’t integrate, use geometry for linear curves.
5.7 Problem-solving templates (to avoid losing marks)
Template A: Derive demand → elasticity → welfare
- Write demand function (Q(p)) or inverse demand (p(Q)).
- Compute elasticity at relevant point:
[
\epsilon = \frac{dQ}{dp}\cdot \frac{p}{Q}
] - Determine how price changes affect revenue:
- revenue is (pQ), check sign of (d(pQ)).
- For welfare:
- use CS/PS with geometry or integrals if required.
Template B: Firm supply and equilibrium
- derive (MC(q))
- set (p=MC(q)) for output choice
- verify production condition (p\ge AVC)
- identify where the supply starts (shutdown threshold)
- aggregate to market supply if needed
- solve market equilibrium with demand
Template C: Monopoly output and markup
- write revenue and marginal revenue
- set (MR=MC)
- set price from demand at (q^*)
- compute welfare relative to competitive benchmark using DWL triangle
- apply elasticity rule if asked:
[
\frac{p-MC}{p}=\frac{1}{|\epsilon|}
]
Template D: Externality efficiency
- identify private vs social marginal curves
- find efficient output where:
- negative externality: (MB = SMC)
- find market output where:
- negative externality: (MB = PMC)
- compute Pigouvian tax:
[
t = SMC – PMC
] - state welfare direction: overproduction/underproduction.
5.8 Common exam pitfalls (and how to correct them)
- Mixing up MC and AC
- MC intersects AC at its minimum.
- MC affects output choice; AC affects profit comparison.
- Forgetting shutdown condition
- In short run, firms may produce nothing if price doesn’t cover AVC.
- Confusing tax incidence with statutory burden
- who pays depends on elasticities, not on “who remits” tax.
- Drawing MR like demand
- MR is below demand for a downward sloping demand curve with typical linear forms.
- Assuming monopoly is always “inefficient” without stating why
- you must connect to welfare wedge (output reduction and DWL).
5.9 A full exam-style synthesis problem (integrated practice)
Consider a competitive market for a good with:
- Inverse demand:
[
p = 120 – Q
] - Private marginal cost equals:
[
MC = Q
] - External marginal damage is constant:
[
MD = 30
]
So:
[
SMC = PMC + MD = Q + 30
]
Part 1: Competitive equilibrium (no externality internalisation)
Competitive condition:
[
p = PMC \Rightarrow 120 – Q = Q
\Rightarrow 120 = 2Q
\Rightarrow Q_m = 60
]
Price:
[
p_m = 120 – 60 = 60
]
Part 2: Efficient equilibrium
Efficient condition:
[
p = SMC \Rightarrow 120 – Q = Q + 30
\Rightarrow 90 = 2Q
\Rightarrow Q_{eff} = 45
]
Price:
[
p_{eff} = 120 – 45 = 75
]
So the market overproduces:
[
60 > 45
]
Deadweight loss arises from the production between 45 and 60.
Part 3: Pigouvian tax
Tax equals marginal external damage:
[
t = 30
]
This increases firms’ effective marginal cost to shift supply so that equilibrium output becomes 45.
If the exam asks for welfare loss with linear curves, you would compute the DWL triangle area:
[
DWL = \frac{1}{2} \times (t) \times (Q_m – Q_{eff})
= \frac{1}{2} \times 30 \times (60-45)
= 15 \times 15
= 225
]
(Units depend on the price/output scaling in the question, but the method is standard.)
This integrated example is representative of ECON2000 questions that combine demand, costs, externalities, and welfare computation.
5.10 South African university and TVET relevance: how exam questions are typically framed
Across many South African institutions (universities and TVET colleges that teach intermediate micro), exam questions frequently:
- provide a linear or simple functional form,
- ask you to compute equilibrium quantities and prices,
- require graph interpretation (often labelled key points),
- ask for welfare/efficiency reasoning,
- sometimes embed policy context (taxation, regulation, externalities).
A typical pattern:
- Given (p(Q)) and (C(q)), compute:
- competitive equilibrium or monopoly outcome,
- profit,
- welfare changes under a tax or regulation,
- policy instrument to achieve efficiency.
Because the course is “intermediate,” you are expected to show:
- correct derivations,
- correct substitution into equilibrium conditions,
- clear interpretation in words.
5.11 Final checklist for ECON2000 written answers
Before submitting your exam script, verify:
- All curves are identified (demand, supply, MC, MR, AC, AVC, SMC/PMC).
- First-order conditions are stated correctly:
- competition: (p=MC) (and shutdown check)
- monopoly: (MR=MC)
- externality efficiency: (MB=SMC) for negative externality
- You compute the right equilibrium and use it for welfare.
- You interpret results (price up/down, quantity up/down, efficiency improved/worsened).
- You include unit consistency and correct triangle areas if linear.
This checklist tends to convert “partial understanding” into high marks because exam graders reward both correctness and reasoning structure.
Conclusion: The ECON2000 microeconomics map
Intermediate Microeconomics is a toolkit course. The centre of gravity is the set of marginal conditions—how consumers equate MRS to price ratios, how competitive firms equate price to marginal cost, how monopolies equate marginal revenue to marginal cost, and how welfare efficiency aligns marginal benefits with marginal social costs (or social marginal benefits). Once you master the translation between words, graphs, and algebra—and once you practise decomposing policy impacts into incidence and deadweight loss—you will be able to tackle the majority of ECON2000 exam questions successfully, including those grounded in South African policy and real-world market contexts.
