JC
HUB
HUB
Supply & Demand
Ch29
LO 3.3
LO 3.3
📌 Tap each section to expand it.
📈 Chapter 29 — Supply & Demand
Demand
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Demand — the quantity consumers are willing and able to buy at different pricesCreated by buyers in a market
Law of Demand — price rises, quantity demanded falls. Price falls, quantity demanded rises.Price and demand move in opposite directions
Demand Curve — slopes downward from left to right
Increases demand: lower price, higher income, positive advertising, rise in price of a substitute, fall in price of a complement, stronger consumer preference
Decreases demand: higher price, lower income, new cheaper substitute, VAT increase, negative reviews
Top Tip: “Scarcity” or “less demand” alone = zero marks. You must explain why the factor changes demand. No one-word answers.
Supply
▼
Supply — the quantity sellers are willing and able to sell at different pricesCreated by sellers in a market
Law of Supply — price rises, quantity supplied rises. Price falls, quantity supplied falls.Price and supply move in the same direction
Supply Curve — slopes upward from left to right
Increases supply: higher selling price, lower production costs, new technology, VAT reduction, good weather
Decreases supply: lower selling price, higher production costs, strikes, natural disaster, tax increase
Top Tip: The price is what sellers receive, not what it costs them. Higher selling price = more profit = firms supply more.
Substitutes & Complements
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Substitute Good — an alternative good used for the same purposeExample: Pepsi for Coca-Cola. Samsung Galaxy for iPhone.
Complementary Good — a good used together with another goodExample: a phone case for a phone. Cereal and milk.
Top Tip: Use “alternative” or “replacement” when explaining a substitute. “Similar” or “next best thing” alone = 1 mark only. Always include an example.
Market Equilibrium & Prices
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Equilibrium — where demand equals supply. Where the curves cross.The market is balanced at this price and quantity
Shortage — demand > supply. Prices increase (goods are scarce).
Surplus — supply > demand. Prices decrease (unsold goods).
Top Tip: Always include the € sign for price and the word “units” for quantity. If 000s, write the full figure (600,000 units not 600).
📚 Tap any term to reveal its definition.
Demand
Market
Any place where buyers and sellers interact to exchange goods or services.
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Demand
The quantity of a good or service consumers are willing and able to buy at different prices.
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Law of Demand
When price rises, quantity demanded falls. When price falls, quantity demanded rises. Price and demand move in opposite directions.
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Demand Curve
A line on a diagram sloping downward from left to right, showing the relationship between price and quantity demanded.
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Supply
Supply
The quantity of a good or service sellers are willing and able to sell at different prices.
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Law of Supply
When price rises, quantity supplied rises. When price falls, quantity supplied falls. Price and supply move in the same direction.
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Supply Curve
A line on a diagram sloping upward from left to right, showing sellers supply more at higher prices.
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Substitutes & Complements
Substitute Good
An alternative good that can be used for the same purpose. Example: Pepsi is a substitute for Coca-Cola.
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Complementary Good
A good used together with another good. Example: a phone case is complementary to a phone.
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Equilibrium & Price Changes
Market Equilibrium
The price and quantity where demand equals supply. Where the curves cross on a diagram.
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Shortage (Scarcity)
Demand is greater than supply. Not enough goods. Prices increase.
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Surplus
Supply is greater than demand. Unsold goods. Prices decrease.
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Black Market
A market where transactions are illegal and unrecorded. No tax is paid. Consumers lose consumer rights.
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Remember: No one-word answers. Always use the two-prong rule: identify + elaborate.
🎦 Chapter 29 video walkthroughs. Watch alongside your textbook.
How to Plot a Demand Curve
Step-by-step guide to plotting demand data from a table on to a graph.
Showing Shifts of a Demand Curve
How factors such as price changes, income and substitutes cause the demand curve to shift left or right.
Plotting and Identifying Market Equilibrium
How to plot both curves from a table and find the equilibrium price and quantity where they cross.
⚡ Work through the pile. Tap to flip. Tick when you know it. Cross to send back.
🅻 Test yourself. All examples use different brands from the exam papers so you can practise fresh scenarios. Pick a topic or try all.
📄 Past paper questions with model answers.
Key Skills Tested (2019-2025)
① Identify substitutes vs complementary goods with examples
② Explain factors that increase or decrease demand and supply
③ Identify prices and quantities from a demand and supply curve graph
④ Draw and label a demand and supply curve graph from a table
⑤ Explain how changes in demand or supply impact market prices
② Explain factors that increase or decrease demand and supply
③ Identify prices and quantities from a demand and supply curve graph
④ Draw and label a demand and supply curve graph from a table
⑤ Explain how changes in demand or supply impact market prices
📄 2019 Paper — Q16(a) 21m
(i) Quantity supplied at €20? (ii) Quantity demanded at €8? (iii) Equilibrium price? (iv) Impact of factors on demand?
(i) 80 units (3m) • (ii) 100 units (3m) • (iii) €16 (3m)
(iv):
(iv):
| Increased | Decreased | |
|---|---|---|
| Reduction in price of books | ✓ | |
| Increase in taxes (VAT) | ✓ | |
| Broadband rollout in Wicklow | ✓ | |
| Eason's opening in town | ✓ |
Top Tip: Always include the € sign. Eason's is a substitute. Broadband makes online alternatives easier to access, decreasing demand for the local bookshop.
📄 2022 Paper — Q16(c) 25m
(i) Draw D&S curves from table (12m). (ii) Equilibrium price & quantity (5m). (iii) Sub or comp for PS5 (8m).
(i) 5 points per curve, 1m each + 1m label per curve = 12m.
(ii) Eq Price: €400. Eq Quantity: 600,000 units.
(iii) Xbox = Substitute. PS5 Controller = Complementary. Headset = Complementary. Gaming Chair = Complementary.
(ii) Eq Price: €400. Eq Quantity: 600,000 units.
(iii) Xbox = Substitute. PS5 Controller = Complementary. Headset = Complementary. Gaming Chair = Complementary.
Top Tip: Missing the € sign or writing “600” instead of “600,000 units” loses marks. Units are in 000s on the graph.
📄 2023 Paper — Q18(b) 27m
(i) Eq qty, eq price, qty at €1,600 (9m). (ii) Explain substitute (4m). (iii) Reduced supply impact on price (5m). (iv) Supply factors (9m).
(i) Eq qty: 80 million units. Eq price: €1,000. Qty at €1,600: 20 million units.
(ii) An alternative good used for the same purpose. Example: Samsung Galaxy. (3m + 1m)
(iii) Prices would increase because fewer iPhones available creates scarcity, so buyers pay more.
(iv) Decreased cost → increased supply. Strike → decreased. Storm damage → decreased.
(ii) An alternative good used for the same purpose. Example: Samsung Galaxy. (3m + 1m)
(iii) Prices would increase because fewer iPhones available creates scarcity, so buyers pay more.
(iv) Decreased cost → increased supply. Strike → decreased. Storm damage → decreased.
Top Tip: Write “increase” not arrows. Must write a sentence for the reason. Need “m” or “million” with the quantity.
📄 2024 Paper — Q18(c) 21m
(i) Draw and label D&S curves, title, label axes (15m). (ii) Equilibrium price & quantity (6m).
(i) Title (1m), x-axis label (1m), y-axis label (1m), 5 demand points (5m), 5 supply points (5m), D label (1m), S label (1m) = 15m.
(ii) Eq Price: €2.00. Eq Quantity: 600,000 units.
(ii) Eq Price: €2.00. Eq Quantity: 600,000 units.
Top Tip: Units are in 000s, so 600 on the graph = 600,000 units. Always write the full figure with the word “units”.
📄 2025 Paper — Q12 6m
Explain two factors which affect the demand for Taylor Swift concert tickets.
Any two, each with identification + elaboration:
Price — if tickets become too expensive, fewer people will be willing to buy them, so demand falls.
Consumer income — if household income rises, more people can afford tickets, so demand increases.
Advertising — heavy promotion increases awareness, so more people want to attend.
Price of substitutes — if cheaper entertainment becomes available, people switch and demand for tickets falls.
Consumer preferences — Taylor Swift is popular among fans, increasing demand for her concerts.
Price — if tickets become too expensive, fewer people will be willing to buy them, so demand falls.
Consumer income — if household income rises, more people can afford tickets, so demand increases.
Advertising — heavy promotion increases awareness, so more people want to attend.
Price of substitutes — if cheaper entertainment becomes available, people switch and demand for tickets falls.
Consumer preferences — Taylor Swift is popular among fans, increasing demand for her concerts.
Top Tip: “Consumer preference” alone = 1 mark. You must explain why it affects demand for full marks. No one-word answers.
