ECO1010F Microeconomics I Exam Notes (University of Cape Town)

Microeconomics I (ECO1010F) develops the core tools for analyzing individual markets: how consumers make choices, how firms decide output, and how prices coordinate economic activity. These exam notes focus on the syllabus-style concepts commonly assessed in Microeconomics I—demand and supply, consumer theory, elasticity, market structures, and the basics of welfare and policy. Throughout, examples are tailored to contexts that frequently appear in South African university coursework.

This guide is designed to be exam-ready: it includes definitions, step-by-step methods for typical calculations, interpretation of graphs, and practice-style mini-scenarios that mirror how questions are often framed in South African Economics courses.

1. Microeconomics Foundations for ECO1010F: Markets, Scarcity, Choice, and the Role of Prices

Microeconomics studies how economic units—households (consumers), firms, and government—make decisions under scarcity. The defining feature of microeconomics is that it focuses on specific markets (e.g., bread, electricity, labour markets, housing) rather than the whole economy. In ECO1010F, much of the course uses models: simplified representations of reality that allow clear cause-and-effect reasoning.

1.1 Core concepts: scarcity, opportunity cost, rational choice

A starting point in most Microeconomics I exams is the idea that individuals face trade-offs.

• Scarcity means resources are limited relative to wants.
• Opportunity cost is the value of the next-best alternative forgone.
• Rational choice (in micro models) typically means choosing options that maximize something under constraints.

A common exam implication: when a variable changes, you must be clear about whether it affects:

1. Preferences (what people want),
2. Constraints (budgets/technology),
3. Prices (relative trade-offs),
4. Expectations (future uncertainty).

1.2 What “markets” mean in microeconomics

A market is the interaction between buyers and sellers for a good or service. Microeconomics uses the market as an organizing device:

• Buyers respond to prices and income (demand).
• Sellers respond to prices, costs, and technology (supply).
• The equilibrium price and quantity summarize where plans of buyers and sellers are consistent.

In exam settings, you may be given a scenario like:

• “The price of petrol rises due to fuel taxes.”
  You then predict:
• higher costs for transport-intensive firms,
• changes in consumer expenditures (demand shifts), and
• possible second-round effects (e.g., demand for certain food items falls).

You usually are not asked to model every chain reaction, but you must identify the immediate mechanism: relative price changes.

1.3 Economic models, assumptions, and ceteris paribus reasoning

Most microeconomics problems are built on the logic of ceteris paribus (“other things equal”). For graph-based exam questions:

• If only the price of the good changes, then you move along the demand or supply curve.
• If something else changes (income, tastes, input prices, technology), then the curve shifts.

You should be able to answer questions like:

• If income increases, does the demand curve shift?
• If a tax is introduced, does supply shift (typically yes), and how?
• If technology improves, does supply increase for each price (shift right)?

1.4 Supply and demand as the “language” of the course

ECO1010F often begins or reintroduces:

• Demand curve: downward sloping relation between price and quantity demanded (holding other factors constant).
• Supply curve: upward sloping relation between price and quantity supplied (holding other factors constant).

To be exam-ready, you need these skills:

1. Identify whether a change causes a movement or a shift.
2. Predict direction (increase/decrease).
3. Compute equilibrium changes using algebra when given linear functions.
4. Interpret graphs under taxes, subsidies, or price controls.

1.5 Demand and supply equilibrium: interpreting graphs correctly

Equilibrium is where:
[
Q_d(P) = Q_s(P)
]
Graphically:

• Demand and supply curves intersect at equilibrium.
• The equilibrium price is the price that clears the market: at that price, buyers want exactly what sellers are willing to provide.

Exam trap: confuse “equilibrium” with “where the curves cross only in one sense.” If demand and supply shift due to other factors, the intersection changes. In particular:

• A demand shift changes equilibrium price and quantity.
• A supply shift also changes both, but in different directions depending on which direction each shift occurs.

1.6 A worked equilibrium example (linear curves)

Assume demand and supply:
[
Q_d = 120 – 2P,\quad Q_s = 30 + 2P
]
Set equal:
[
120 – 2P = 30 + 2P
]
[
120 – 30 = 4P
\Rightarrow 90 = 4P
\Rightarrow P^* = 22.5
]
Then:
[
Q^* = 120 – 2(22.5) = 120 – 45 = 75
]

When the exam asks for “equilibrium price and quantity,” your response should include:

• the setting equality,
• the algebra,
• the computed values.

1.7 Elasticity as the key to prediction

Microeconomics is often about how sensitive quantity is to price or other variables. That leads to:

• Price elasticity of demand
• Price elasticity of supply
• Income elasticity
• Cross-price elasticity

Elasticity is not just a number: it helps predict how much the equilibrium changes when there is a policy shock (tax) or a demand shock (technology, tastes).

2. Demand, Elasticity, and Consumer Choice: How Individuals Respond to Prices

ECO1010F typically tests demand theory in two connected ways:

1. Demand curves and elasticity (market-level response)
2. Consumer choice via utility maximization and/or budget constraints (individual-level response)

Even when exams start with graphs, they often reward understanding of underlying logic.

2.1 Demand: determinants and the idea of shifts

Demand for a good depends on:

• Price of the good (movement along curve)
• Income (shifts curve)
• Tastes and preferences
• Prices of substitutes and complements
• Expectations about future prices
• Number of buyers

Substitutes: if price of substitute rises, demand for your good increases (demand shifts right).
Complements: if price of complement rises, demand for your good decreases (demand shifts left).

A classic micro example:

• If the price of coffee rises, demand for tea might rise (substitution).
• If the price of sugar rises, demand for tea might fall (complement/increased cost of tea consumption).

2.2 Movements vs shifts: exam-critical distinction

Use this checklist:

If the variable is the good’s own price (P):

• Move along the demand curve.

If any other determinant changes:

• Shift the demand curve.

Similarly for supply:
If the variable is the good’s own price (P):

• Move along supply.

If an input price, technology, or regulation changes:

• Shift supply.

2.3 Elasticity: definitions and interpretations

Price elasticity of demand (PED):
[
\varepsilon_d = \frac{%\Delta Q_d}{%\Delta P}
]

Common exam interpretations:

• (|\varepsilon_d| > 1): elastic demand (quantity responds strongly).
• (|\varepsilon_d| < 1): inelastic demand (quantity responds weakly).
• (|\varepsilon_d| = 1): unit elastic.

Demand is typically downward sloping, meaning:

• the elasticity is often negative if you use the sign,
• many exams focus on absolute value.

Important: elasticity differs along the curve if the curve is not linear in the relevant way.

2.4 Point elasticity vs arc elasticity

Many calculations in exams use arc elasticity between two points:
[
\varepsilon_{arc} = \frac{(Q_2 – Q_1)/\left(\frac{Q_1+Q_2}{2}\right)}{(P_2 – P_1)/\left(\frac{P_1+P_2}{2}\right)}
]
But some courses also teach point elasticity:
[
\varepsilon_d = \frac{dQ}{dP}\cdot\frac{P}{Q}
]
If the exam states “between points,” arc elasticity is usually the expectation.

2.5 Elasticity example with full steps

Suppose:

• Price increases from (P_1=10) to (P_2=12)
• Quantity decreases from (Q_1=100) to (Q_2=90)

Arc elasticity:
[
%\Delta Q = \frac{90-100}{(100+90)/2} = \frac{-10}{95}=-0.1053
]
[
%\Delta P = \frac{12-10}{(10+12)/2} = \frac{2}{11}=0.1818
]
[
\varepsilon_{arc} = \frac{-0.1053}{0.1818}=-0.579
]
Absolute value (0.579 < 1), so demand is inelastic.

Exam interpretation: a relatively small percentage decrease in quantity compared to the percentage increase in price.

2.6 Total revenue test (fast conceptual skill)

A useful exam shortcut:

• If demand is elastic, price up (\Rightarrow) total revenue falls.
• If demand is inelastic, price up (\Rightarrow) total revenue rises.
• If demand is unit elastic, total revenue unchanged.

While you must not rely solely on this test for rigorous calculations, it helps interpret graph reasoning questions.

2.7 Elasticity and determinants

Demand tends to be more elastic when:

• there are many substitutes,
• the good is a luxury rather than a necessity,
• the time horizon is longer (people can adjust habits),
• the share of income spent on the good is large.

In supply:

• supply is more elastic when firms can adjust production inputs quickly,
• if production is flexible and capacity is available.

2.8 Consumer theory: preferences, utility, and budget constraints

Microeconomics I often introduces:

• Utility function as a representation of preferences.
• Budget constraint:
  [
  p_x x + p_y y \le m
  ]
  where (x,y) are quantities of goods, (p_x,p_y) are prices, (m) is income.

A standard exam task:

• identify the feasible set,
• find the optimal bundle given utility.

2.9 Utility maximization and marginal utility logic

A common framework uses the idea:

• the consumer chooses where the trade-off between goods matches their relative prices.

For two goods:

• Consumer’s willingness to trade one good for another is summarized by marginal rate of substitution (MRS).
• Market trade-off is given by relative price:
  [
  \text{MRS} = \frac{MU_x}{MU_y} = \frac{p_x}{p_y}
  ]

If exam questions use Lagrangian methods, you may see:
[
\max U(x,y)\quad \text{s.t.}\quad p_x x + p_y y = m
]
Then:
[
\mathcal{L}=U(x,y)+\lambda(m-p_x x-p_y y)
]
and solve first-order conditions.

Even if the exam doesn’t ask you to set up Lagrangians, conceptually you should know:

• the optimum occurs where marginal trade-offs align with prices.

2.10 Indifference curves and diminishing marginal rate of substitution

Indifference curves represent combinations that yield the same utility.
Key properties:

• higher indifference curves correspond to higher utility,
• indifference curves are downward sloping for “normal” goods,
• convexity reflects diminishing marginal rate of substitution.

Graph questions may ask:

• “If income rises, what happens to the budget line?”
  Answer: it shifts outward parallel if prices are constant.

• “If price of good (x) rises, what happens?”
  Answer: budget line pivots inward around the intercept for the other good.

2.11 Worked consumer choice example with Cobb-Douglas utility

Let utility:
[
U(x,y)=x^{0.5}y^{0.5}
]
Budget: (p_x=2), (p_y=1), income (m=60).

For Cobb-Douglas with equal exponents:

• the optimal shares are:
  [
  \text{Spend half income on } x,\quad \text{half on } y
  ]
  So:
• Expenditure on (x): (m/2=30)
  [
  2x=30 \Rightarrow x=15
  ]
• Expenditure on (y): (m/2=30)
  [
  1y=30 \Rightarrow y=30
  ]

Exam-worthy conclusion:

• when prices change, the optimal consumption changes,
• but the relative expenditure shares remain proportional for Cobb-Douglas.

2.12 Normal goods, inferior goods, and income effects

Consumer choice under income changes yields:

• Normal good: demand increases with income.
• Inferior good: demand decreases with income.

In an exam scenario:

• Suppose a good is an inferior good. If income rises due to wage increases, the demand shifts left.

2.13 Substitution and income effects (conceptual decomposition)

When a price changes, consumption changes for two reasons:

1. Substitution effect: relative price change changes relative attractiveness.
2. Income effect: price change alters real purchasing power.

For typical normal goods:

• substitution effect tends to move demand down (price up reduces quantity).
• income effect may reinforce or partially offset depending on whether the good is normal or inferior.

This is often asked in conceptual form rather than calculation.

2.14 Demand curve from consumer optimization (intuition)

A demand curve can be derived by:

• choosing optimal (x) for each price (p_x),
• tracing the optimal (x(p_x)).

This connects micro-level choice to market-level demand.

3. Producers, Costs, and Market Supply: Firms, Technology, and the Logic of Pricing

Microeconomics I typically shifts from consumers to firms. The core producer side includes:

• production functions and technology,
• costs (fixed vs variable),
• marginal and average costs,
• profit maximization,
• supply decisions.

3.1 Production and technology: inputs to outputs

A production function maps inputs to output:
[
q=f(K,L)
]
where:

• (K) = capital,
• (L) = labour,
• (q) = output.

In many exam questions, technology is summarized indirectly via marginal products or via cost functions.

3.2 Short-run vs long-run: why it matters

Key distinction:

• Short run: at least one input is fixed (often capital).
• Long run: all inputs are variable.

This matters for cost curves:

• Short-run costs include fixed costs,
• long-run planning allows choosing optimal plant scale.

3.3 Costs: fixed, variable, average, marginal

Let:

• fixed cost (FC) (does not change with output),
• variable cost (VC(q)),
• total cost:
  [
  TC(q)=FC+VC(q)
  ]
  Define:
• Average cost:
  [
  AC(q)=\frac{TC(q)}{q}
  ]
• Marginal cost:
  [
  MC(q)=\frac{dTC(q)}{dq}
  ]
  In discrete form, MC is approximated by:
  [
  MC \approx \frac{\Delta TC}{\Delta q}
  ]

A central graph relationship:

• If (MC < AC), then (AC) is falling.
• If (MC > AC), then (AC) is rising.
• (MC=AC) at the minimum point of (AC).

Exams often test whether students can interpret these relationships.

3.4 Worked cost example with marginal and average costs

Suppose:

• (FC=40)
• (VC(q)= q^2 + 5q)

Then:
[
TC(q)=40 + q^2 + 5q
]
Marginal cost:
[
MC(q)=\frac{dTC}{dq}=2q + 5
]
Average cost:
[
AC(q)=\frac{40 + q^2 + 5q}{q} = \frac{40}{q} + q + 5
]

If asked to compute at (q=5):

• (TC(5)=40+25+25=90)
• (AC(5)=90/5=18)
• (MC(5)=2(5)+5=15)

Interpretation:

• (MC(5)=15 < AC(5)=18), so at that output level, AC is decreasing as output rises.

3.5 Profit maximization: the main rule

Profit:
[
\pi(q)=TR(q)-TC(q)=P\cdot q – TC(q)
]
For competitive markets where the firm is a price taker (in standard Micro I):

• the firm chooses (q) to maximize profit.
• The key decision rule:
  • produce where (MR=MC).
    In price-taking competitive markets:
• (MR=P), so:
  [
  P = MC(q^*)
  ]

Short-run shutdown condition:

• if price is below minimum AVC (average variable cost), producing yields losses larger than shutting down.

3.6 Supply in competitive markets: from MC above shutdown

In the short run, a competitive firm supplies output where:

• (P \ge AVC) and
• (P = MC).

So market supply is found by horizontal summing individual firm supplies.

Exam tasks:

• Determine the firm’s supply function given cost structure.
• Then sum across identical firms.

3.7 Example: deriving supply from a simple cost function

Let:

• (TC(q)=40 + 0.5q^2)
  Then:
  [
  MC(q)=\frac{dTC}{dq}=q
  ]
  Assume price (P) is high enough such that producing is worthwhile.

Set (P=MC):
[
P=q \Rightarrow q=P
]
So the supply for one firm is (q(P)=P), with the domain where (P) is above shutdown threshold.

If there are two identical firms:

• market supply:
  [
  Q(P)=q_1(P)+q_2(P)=P+P=2P
  ]

When exams ask for market equilibrium with demand (Q_d=a-bP), you substitute (Q(P)) to solve for (P) and (Q).

3.8 Substitution from consumer side vs supply side: intuition

On the consumer side, demand depends on prices and income. On the firm side, supply depends on:

• technology and costs,
• input prices,
• taxes/subsidies,
• regulatory constraints.

A policy like a per-unit tax (t) typically raises the cost of producing each unit, shifting supply up/left. Many exam questions ask for:

• who bears the tax burden,
• changes in equilibrium.

3.9 Tax incidence and relative elasticities (core exam theme)

Even without full derivations, you must understand:

• the side with more inelastic demand or supply bears a larger portion of the tax burden.

Graphically:

• A tax creates a wedge between the price paid by consumers and the price received by producers.
• The tax revenue is wedge times quantity sold.

3.10 Worked tax incidence with linear supply and demand

Consider:
[
Q_d=120-2P_c
]
[
Q_s=30+2P_p
]
where (P_c) is consumer price and (P_p) is producer price. A per-unit tax (t) satisfies:
[
P_c = P_p + t
]

Let (t=10). Then (P_c = P_p + 10).

Equilibrium requires (Q_d = Q_s):
[
120 – 2(P_p+10) = 30 + 2P_p
]
[
120 – 2P_p – 20 = 30 + 2P_p
]
[
100 – 2P_p = 30 + 2P_p
]
[
70 = 4P_p \Rightarrow P_p = 17.5
]
Then (P_c=27.5).

Quantity:
[
Q = 120 – 2(27.5) = 120 – 55 = 65
]
Tax revenue:
[
TR_{tax} = t\cdot Q = 10\cdot 65 = 650
]

Exam skills:

• keep the distinction between consumer and producer prices,
• compute equilibrium quantity,
• compute tax revenue,
• interpret burden via changes relative to pre-tax equilibrium.

4. Market Structures and Strategic Pricing: Perfect Competition, Monopoly, and Beyond

A major portion of Microeconomics I typically covers market structures. Even if the course focuses mainly on competition vs monopoly, you must understand:

• how firm behavior changes with market power,
• how price and quantity are determined,
• welfare implications.

4.1 Perfect competition: price-taking behaviour and zero economic profit in long run

In perfect competition:

• many firms,
• identical products,
• firms are price takers,
• entry and exit occur.

In the short run:

• firms can earn positive or negative economic profits.
  In the long run:
• economic profits are competed away,
• firms earn zero economic profit (in economic terms) if entry/exit is free.

Competitive equilibrium:

• determined by market supply and demand,
• at the firm level by (P=MC) for output choice.

Welfare:

• under standard assumptions, competitive markets can be efficient in the sense that price equals marginal cost, resembling the condition for efficiency.

4.2 Monopoly: single seller, barriers, and the role of marginal revenue

In monopoly:

• one firm sells the product,
• barriers to entry exist,
• the firm faces the market demand curve (not perfectly elastic).

Key implication:

• The firm’s marginal revenue (MR) lies below demand (because lowering price to sell more requires reducing price on all units).

Profit maximization:

• choose (q) where:
  [
  MR = MC
  ]
  Then set price using demand:
  [
  P \text{ is read off from } D(q)
  ]

An exam common question: compare monopoly output to competitive output.

• monopoly typically restricts output (lower quantity) and charges a higher price.

4.3 Monopoly worked example with linear demand and cost

Let demand:
[
P(Q)=100 – Q
]
Total revenue:
[
TR(Q)=P\cdot Q=(100-Q)Q=100Q – Q^2
]
Marginal revenue:
[
MR(Q)=\frac{dTR}{dQ}=100 – 2Q
]
Suppose cost:
[
TC(Q)=20Q \quad \Rightarrow MC=20
]

Set (MR=MC):
[
100 – 2Q = 20 \Rightarrow 2Q=80 \Rightarrow Q_m=40
]
Price from demand:
[
P_m=100-40=60
]

How would this compare with competition?
In competition, typically:
[
P=MC=20
]
But market demand:
[
20=100-Q \Rightarrow Q_c=80
]
So:

• monopoly: (Q_m=40), (P_m=60)
• competition: (Q_c=80), (P_c=20)

This provides a clear exam comparison: monopoly output is lower and price is higher.

4.4 Deadweight loss and welfare under monopoly

Welfare analysis compares benefits and costs:

• consumer surplus and producer surplus,
• deadweight loss from reduced output relative to efficient levels.

In the monopoly example above:

• efficient output often corresponds to where (P=MC) (i.e., (Q_c) under the model).
• monopoly output (Q_m) is below (Q_c), so there is a reduction in total surplus.

Exam interpretation:

• deadweight loss is the area between the demand curve and marginal cost curve over the range of reduced quantity.
• tax or monopoly analysis often ties to welfare distortions.

4.5 Price discrimination (basic intuition)

Some Micro I syllabi include:

• monopoly can sometimes reduce welfare loss by charging different prices to different consumers.

Forms:

• First-degree (perfect) discrimination: monopoly captures all consumer surplus.
• Second-degree: quantity discounts, self-selection via menu of prices.
• Third-degree: different prices across identifiable groups.

Even if detailed calculations are not required, exams may ask conceptual questions:

• when is discrimination possible?
• what is the constraint (must be able to prevent resale and identify groups)?

4.6 Oligopoly and strategic interaction (if covered)

If the course touches oligopoly:

• firms face interdependence,
• pricing decisions are strategic rather than independent.

But Microeconomics I may not go deep into Nash equilibrium; it may focus on qualitative consequences:

• collusion incentives,
• game-theoretic reasoning.

You should be ready to:

• explain why concentrated markets may yield higher prices and reduced output,
• connect to barriers to entry and market power.

4.7 Entry and contestable markets (conceptual link)

Market power is shaped by:

• barriers to entry (legal, cost, control of inputs),
• ease of entry (contestability).

Even if not heavily quantitative, exams may ask:

• “What happens to monopoly profits if entry becomes easier?”

Answer:

• increased entry pushes prices toward competitive levels over time,
• profits erode.

5. Welfare, Government Policy, Market Failures, and Exam-Style Problem Solving

The final major theme in Microeconomics I is often welfare analysis and policy. ECO1010F frequently emphasizes:

• consumer surplus and producer surplus,
• efficiency and deadweight loss,
• effects of taxes, subsidies, price floors and ceilings,
• externalities and basic market failure reasoning (depending on syllabus).

This section integrates those tools with exam-style solution strategies.

5.1 Consumer surplus and producer surplus

Consumer surplus (CS):

• difference between what consumers are willing to pay (demand curve) and what they actually pay (market price).
  Graphically:
• CS is the area under the demand curve and above the price line (up to quantity sold).

Producer surplus (PS):

• difference between what producers receive (price) and their willingness to supply (marginal cost / supply curve).
  Graphically:
• PS is the area above the supply curve and below the price line.

Under many models:
[
\text{Total surplus} = CS + PS
]

5.2 Welfare under taxes: deadweight loss and incidence

Consider a per-unit tax (t). Compared to no tax:

• quantity decreases from (Q^*) to (Q_t),
• the wedge between consumer and producer price causes transfers to government.

Welfare components:

• CS decreases,
• PS decreases,
• government revenue increases,
• deadweight loss arises from the reduced trades that were mutually beneficial.

Deadweight loss:

• loss of total surplus not captured as government revenue.

Exam method:

1. Compute new equilibrium (P_c, P_p, Q_t).
2. Compute CS and PS changes (often via areas under curves in linear cases).
3. Compute tax revenue.
4. Compute deadweight loss as:
   [
   DWL = (CS_{before}+PS_{before})-(CS_{after}+PS_{after}+TaxRev)
   ]
   In some exams, you compute DWL directly as triangle areas formed by supply-demand geometry.

5.3 Worked welfare effect example using linear geometry

Use demand:
[
Q_d=120-2P_c
]
and supply:
[
Q_s=30+2P_p
]
No tax equilibrium (from earlier derivation with (P_p=P_c)):
Set (120-2P=30+2P):
[
P^=22.5,\quad Q^=75
]

Now with tax (t=10):
We found:
[
P_p=17.5,\quad P_c=27.5,\quad Q_t=65,\quad \text{TaxRev}=650
]

To compute welfare changes, you typically need:

• intercepts for demand and supply in price-quantity space.

Demand:
[
Q=120-2P_c \Rightarrow 2P_c=120-Q \Rightarrow P_c=60-0.5Q
]
So demand intercept at (Q=0) is (P=60).

Supply:
[
Q=30+2P_p \Rightarrow 2P_p=Q-30 \Rightarrow P_p=0.5Q-15
]
Supply intercept at (Q=0) is (P=-15) (not economically meaningful as a price but useful for geometry).

Compute consumer surplus before tax:

• Price is (22.5), quantity (75).
  Demand maximum willingness to pay at (Q=75):
  Demand curve gives:
  [
  P=60-0.5Q=60-0.5(75)=60-37.5=22.5
  ]
  So consistent.

Consumer surplus area:
[
CS_{before}=\frac{1}{2}\times \text{base}\times \text{height}
]
Base = (Q^*=75).
Height = demand intercept (60) minus price (22.5):
[
CS_{before}=\frac{1}{2}\cdot 75\cdot(60-22.5)=37.5\cdot 37.5=1406.25
]

Producer surplus before tax:
Producer surplus is area above supply curve and below price. The supply price at (Q=75) equals price 22.5:
[
P_p = 0.5Q-15 = 0.5(75)-15=37.5-15=22.5
]
Supply curve intersects price axis at negative value; for producer surplus computation in linear form, the “height” corresponds to price minus supply intercept at (Q=0) (which is (-15)).
So height = (22.5-(-15)=37.5).
Base = 75.
[
PS_{before}=\frac{1}{2}\cdot 75\cdot 37.5=1406.25
]
Thus total surplus before tax:
[
TS_{before}=CS_{before}+PS_{before}=2812.5
]

After tax:
Quantity (Q_t=65).
Consumer price (P_c=27.5).
Demand intercept still 60.
[
CS_{after}=\frac{1}{2}\cdot 65\cdot(60-27.5)=32.5\cdot 32.5=1056.25
]

Producer price (P_p=17.5).
Producer surplus height = (17.5-(-15)=32.5).
Base = 65.
[
PS_{after}=\frac{1}{2}\cdot 65\cdot 32.5=1056.25
]

Total surplus after tax plus tax revenue:
[
TS_{after} + \text{TaxRev} = (CS_{after}+PS_{after}) + 650 = (1056.25+1056.25)+650=2112.5+650=2762.5
]
Deadweight loss:
[
DWL = TS_{before} – (CS_{after}+PS_{after}+TaxRev)=2812.5-2762.5=50
]

Interpretation:

• $50 of total surplus disappears due to reduced trade.

This is the kind of multi-step calculation that may appear in exams, particularly if the module covers welfare.

5.4 Price controls: price floors and ceilings

Sometimes the exam includes government intervention:

• Price ceiling: maximum price (binding if set below equilibrium).
• Price floor: minimum price (binding if set above equilibrium).

For a price ceiling below equilibrium:

• quantity demanded exceeds quantity supplied,
• shortage occurs,
• rationing emerges (non-price mechanisms, queues, informal markets).

For a price floor above equilibrium:

• quantity supplied exceeds quantity demanded,
• surplus occurs.

In welfare terms:

• consumer surplus and producer surplus change,
• deadweight loss occurs because mutually beneficial trades are prevented.

If the exam asks for qualitative outcomes, be explicit:

• “Shortage of size (Q_d-Q_s)” or “surplus of size (Q_s-Q_d)” depending on the control.

5.5 Subsidies: similar geometry with welfare gain, but fiscal cost matters

A subsidy per unit (s) lowers the effective price to consumers and/or increases producer received price. In a competitive linear model:

• it can increase output toward efficient levels in some cases.
• but creates government expenditure:
  [
  \text{Gov spending} = s \cdot Q_s
  ]

Welfare comparison depends on:

• whether the subsidy corrects an underlying distortion,
• or creates inefficiency (similar to taxes but reversed).

In most introductory welfare discussions:

• a subsidy increases quantity and can reduce deadweight loss relative to a tax, but you still account for budgetary cost.

5.6 Externalities and the concept of market failure

Microeconomics I often includes at least an introduction to externalities:

• Externality occurs when a party’s actions affect others’ welfare without compensation.
• Negative externality (e.g., pollution) causes socially optimal output to be lower than private output.
• Positive externality (e.g., vaccination, education in some stories) causes socially optimal output to be higher than private output.

Model idea:

• social marginal cost (SMC) is higher than private marginal cost (PMC) under negative externalities.
• social marginal benefit (SMB) is higher than private marginal benefit (PMB) under positive externalities.

Policy responses:

• taxes (Pigouvian taxes) for negative externalities,
• subsidies for positive externalities.

Even if the exam does not require precise tax calculation, you must be able to explain:

• why unregulated markets produce too much/too little,
• how policy aligns private incentives with social efficiency.

5.7 Practical exam problem-solving framework

When faced with an ECO1010F exam question, a repeatable strategy helps avoid errors:

Step 1: Identify the market and the model

• Is it competitive (price-taking) or monopoly (MR=MC)?
• Is it supply/demand with no strategic interaction?
• Are we dealing with taxes/subsidies or price controls?

Step 2: Clarify what changes

• Price change: movement along curve.
• Other determinant change: shift curve.
• In a tax problem, distinguish (P_c) vs (P_p).

Step 3: Compute equilibrium or optimal quantity

• Use algebra for linear functions.
• Use graph reasoning if functions are not given.

Step 4: Translate into welfare or elasticity outcomes

• For elasticity questions, determine responsiveness.
• For welfare, compute CS/PS changes and deadweight loss when required.

Step 5: State results with interpretation

Good exam answers include:

• the computed numeric results when asked,
• the direction of changes,
• the reasoning in one or two sentences.

5.8 Mini case studies (South Africa relevant contexts)

Exams frequently use “real-world” contexts. Even if the specific scenario differs, the micro logic is the same. Here are exam-ready cases that map to core models.

Case A: Electricity tariff increase and demand responsiveness

Assume households face higher electricity prices due to tariff changes. If electricity has few substitutes in the short run:

• demand is relatively inelastic,
• quantity falls less than proportionally,
• total expenditure may rise.

Policy implication:

• if regulators raise tariffs to cover costs, tax burden analogue depends on elasticity.

Graph-wise:

• a price increase leads to downward movement along demand.
• if tariffs also include a change in income (e.g., wage increases), the demand curve might shift right (depends on which factor is specified).

Case B: VAT change and consumer choice under budget constraints

If VAT increases the effective price of a good:

• consumer budget purchasing power falls,
• budget line pivots (price up of one good),
• substitution effect reduces quantity demanded,
• income effect depends on whether the good is normal.

If the good is a basic necessity (often modeled as normal but relatively inelastic), the income effect might reinforce but not be large.

Case C: Fuel price shock and supply costs in transport

If fuel prices rise:

• it increases variable costs for transport firms,
• supply shifts left/up (higher costs at each output).

Market equilibrium:

• transport prices rise,
• quantity of trips decreases,
• the magnitude depends on elasticity of supply and demand.

These case studies match typical exam narrative styles: connect story to mechanism.

5.9 How to handle elasticity and welfare together (common mixed questions)

A mixed exam question can ask:

• “Is demand elastic? How does that affect tax burden?”
  Your logic:

1. Use elasticity to infer which side bears a larger portion.
2. Use equilibrium calculation to compute actual prices.
3. Then interpret results:
   • if demand is inelastic, consumers tolerate a larger price increase,
   • if supply is inelastic, producers cannot reduce output much, so consumers bear more.

Be careful: elasticity arguments are comparative-statistics in direction; equilibrium computations give magnitudes.

5.10 Common exam pitfalls and how to avoid them

• Pitfall 1: Using the sign of elasticity incorrectly.
  • Fix: report elasticity as absolute value or mention negative sign explicitly.
• Pitfall 2: Mixing movement vs shift.
  • Fix: always ask “what exactly changed?”.
• Pitfall 3: Forgetting (MR=MC) rather than (P=MC) for monopoly.
  • Fix: for monopoly, demand curve gives price, but output uses (MR=MC).
• Pitfall 4: Confusing consumer and producer prices under taxes.
  • Fix: write (P_c=P_p+t) before solving.
• Pitfall 5: Welfare computation mistakes (missing triangle geometry).
  • Fix: compute CS and PS using intercepts and the correct quantity, then compute DWL carefully.

5.11 Rapid graph interpretation drills (typical in exams)

When looking at a diagram, practice stating:

1. Direction of shift
2. New equilibrium price and quantity direction
3. Who gains/loses under policy
4. Whether deadweight loss exists and where

For example, under a binding price ceiling:

• equilibrium quantity falls to supply quantity at the ceiling,
• shortage arises equal to difference between demand and supply at the ceiling,
• deadweight loss equals lost surplus from prevented trades.

Under a tax:

• quantity decreases,
• total surplus decreases,
• tax revenue is a transfer (not welfare loss), while DWL is the loss.

5.12 Full integrated practice example (end-to-end)

Suppose a market with:
[
Q_d = 100 – 2P_c,\quad Q_s = 20 + 2P_p
]
and a tax (t=8) such that (P_c=P_p+8).

1) Compute equilibrium
Set (Q_d=Q_s):
[
100-2(P_p+8)=20+2P_p
]
[
100-2P_p-16=20+2P_p
]
[
84-2P_p=20+2P_p
\Rightarrow 64=4P_p
\Rightarrow P_p=16
]
[
P_c=24
]
Quantity:
[
Q=100-2(24)=100-48=52
]

2) Tax revenue
[
TR_{tax}=tQ=8\cdot 52=416
]

3) Interpret

• Consumers pay (P_c=24) while producers receive (P_p=16).
• The wedge is the tax (8).
• Quantity traded is reduced from the pre-tax equilibrium.

If the exam also asks welfare, you would compute pre-tax equilibrium:
Set (P_c=P_p=P):
[
100-2P=20+2P \Rightarrow 80=4P \Rightarrow P^=20,\ Q^=60
]
Then compare surplus before/after.

Even without completing the welfare geometry, the direction is clear:

• tax increases wedge, reduces quantity, causes DWL.

5.13 South Africa-oriented study focus: aligning your practice with local teaching styles

In South African Economics modules (including UCT-style Micro I coverage), exams often emphasize:

• clear definition recall (demand, supply, elasticity, CS/PS),
• the ability to interpret graphs,
• careful algebra on linear models,
• and structured responses that show method, not just final answers.

A practical way to use this guide:

• for each concept, practice one numerical linear example and one conceptual explanation,
• then link the outcome to welfare or policy impact if relevant.

Conclusion (Exam Takeaways)

ECO1010F Microeconomics I is fundamentally about understanding how individual choices aggregate into market outcomes and how policy interventions affect equilibrium, welfare, and efficiency. Mastery requires competence in (i) demand and supply reasoning, (ii) elasticity and sensitivity analysis, (iii) producer cost and profit maximization logic, and (iv) market structure comparisons between competition and monopoly. If you can consistently translate between graphs, algebra, and economic interpretation—especially in taxes, welfare, and elasticity—your performance in Microeconomics I exams becomes highly predictable and controllable.