📚 IGCSE OCR Economics: Worked Examples Explained in Detail | IGCSE OCR 经济：典型例题详解
Mastering IGCSE OCR Economics requires not only memorising theories but also applying them to typical exam questions. This article provides detailed worked examples covering key topics such as demand and supply, elasticity, market failure, and macroeconomic policies. Each example is broken down step by step to demonstrate effective answering techniques, helping you secure high marks.
掌握IGCSE OCR经济学不仅需要记忆理论，还需要将理论应用于典型的考试题目中。本文提供了涵盖供需、弹性、市场失灵和宏观经济政策等关键主题的详细例题解析。每个例题都逐步分解，以展示有效的答题技巧，帮助你获得高分。
1. Demand and Shifts in Demand | 需求与需求移动
Example: In the market for coffee, a major tea brand launches a highly successful advertising campaign highlighting the health benefits of tea. Explain the impact on the demand for coffee, ceteris paribus.
例题：在咖啡市场中，一个主要茶叶品牌发起了一场极其成功的广告宣传活动，强调茶的健康益处。在其他条件不变的情况下，解释这对咖啡需求的影响。
Step 1: Identify the relationship. Tea and coffee are substitutes in consumption. A successful advertising campaign for tea will increase consumers' preference for tea, leading to a rise in the demand for tea.
第一步：确定关系。茶和咖啡是消费中的替代品。茶叶广告的成功会增加消费者对茶叶的偏好，导致茶叶需求增加。
Step 2: Impact on coffee. As more consumers switch to tea, the demand for coffee decreases. This is represented by a leftward shift of the entire demand curve for coffee, from D1 to D2.
第二步：对咖啡的影响。随着更多消费者转向茶，咖啡的需求减少。这表现为咖啡的整个需求曲线向左移动，从D1移动到D2。
Step 3: Market outcome. The leftward shift of the demand curve, with supply unchanged, results in a lower equilibrium price (P1 to P2) and a lower equilibrium quantity (Q1 to Q2) in the coffee market.
第三步：市场结果。在供给不变的情况下，需求曲线向左移动导致咖啡市场的均衡价格下降（从P1降至P2），均衡数量减少（从Q1减至Q2）。
2. Price Elasticity of Demand Calculation | 需求价格弹性计算
Example: The price of a smartphone app falls from £10 to £8, and the quantity demanded rises from 200 to 260 units per week. Calculate the price elasticity of demand (PED) and interpret whether demand is elastic or inelastic.
例题：某款智能手机应用的价格从10英镑降至8英镑，每周需求量从200单位增加到260单位。计算需求的价格弹性（PED），并解释需求是富有弹性还是缺乏弹性。
PED = %Δ Quantity Demanded ÷ %Δ Price
Step 1: Calculate percentage change in quantity demanded. Change = 260 − 200 = 60. %ΔQd = (60 ÷ 200) × 100% = 30%.
第一步：计算需求量变动的百分比。变化量 = 260 − 200 = 60。需求量变动百分比 = (60 ÷ 200) × 100% = 30%。
p 2: Calculate percentage change in price. Change = £8 − £10 = −2. %ΔP = (−2 ÷ 10) × 100% = −20%.
第二步：计算价格变动的百分比。变化量 = 8 − 10 = −2英鎊。价格变动百分比 = (−2 ÷ 10) × 100% = −20%。
Step 3: Compute PED. PED = 30% ÷ −20% = −1.5. Ignoring the negative sign, the value is 1.5.
第三步：计算PED。PED = 30% ÷ −20% = −1.5。忽略负号，数值为1.5。
Step 4: Interpretation. Since 1.5 > 1, demand is price elastic. A small percentage change in price led to a larger percentage change in quantity demanded. The firm's total revenue will move in the opposite direction to the price change (falling price raises total revenue in this case).
第四步：解读。由于1.5 > 1，需求是富有弹性的。价格较小的百分比变动导致了需求量较大的百分比变动。在这种情况下，企业的总收益将与价格变动方向相反（价格下降会使总收益增加）。
3. Effects of an Indirect Tax on the Market | 间接税对市场的影响
Example: The government imposes a specific tax of £2 per unit on sugary drinks. Using a demand and supply diagram, explain the impact on the equilibrium price, quantity, and the tax burden shared by consumers and producers.
例题：政府对含糖饮料征收每单位2英镑的从量税。运用供需图解释这对均衡价格、数量以及消费者和生产者各自承担的税收负担的影响。
Step 1: Impact on supply. The tax increases the costs of production, shifting the supply curve vertically upwards by exactly the amount of the tax, from S to S + tax. Producers are now willing to supply the same quantity only if the price is £2 higher.
第一步：对供给的影响。税收增加了生产成本，使得供给曲线垂直向上移动，移动幅度等于税额，从S移动到S + tax。现在，只有在价格高出2英镑时，生产者才愿意提供相同的数量。
Step 2: New equilibrium. The market price rises from P1 to P2, and the equilibrium quantity falls from Q1 to Q2. The post-tax price consumers pay is P2.
第二步：新的均衡。市场价格从P1上升到P2，均衡数量从Q1下降到Q2。消费者支付的税后价格为P2。
Step 3: Tax incidence. The price paid by consumers has increased, but not by the full £2; the rise is from P1 to P2. Consumers pay (P2 − P1) per unit, while producers receive the net price P3 (which is P2 − the tax). The producer burden is (P1 − P3). The tax revenue collected by the government is the tax per unit multiplied by Q2.
第三步：税收归宿。消费者支付的价格上涨了，但并没有上涨整整2英镑；涨幅为P2 − P1。消费者每单位承担(P2 − P1)，而生产者获得的净价格为P3（即P2减去税额）。生产者负担为(P1 − P3)。政府获得的税收收入为每单位税额乘以Q2。
Step 4: Determinants of burden. The more inelastic the demand relative to supply, the greater the share of the tax borne by consumers. If demand is very inelastic, most of the tax is passed on to consumers.
第四步：负担的决定因素。相对于供给，需求越缺乏弹性，消费者承担的税收份额就越大。如果需求非常缺乏弹性，大部分税收会转嫁给消费者。
4. Externalities and Market Failure | 外部性与市场失灵
Example: A factory producing chemicals discharges waste into a river, damaging the fishing industry downstream. Explain how this negative production externality leads to market failure.
例题：一家化工厂将废物排入河流，损害了下游的渔业。解释这种负生产外部性如何导致市场失灵。
Step 1: Define the externality. The pollution imposes an external cost on third parties (fishermen) that is not reflected in the factory's private costs. The marginal social cost (MSC) exceeds the marginal private cost (MPC) by the marginal external cost.
第一步：定义外部性。污染给第三方（渔民）带来了外部成本，而该成本并未反映在工厂的私人成本中。边际社会成本（MSC）比边际私人成本（MPC）高出边际外部成本。
Step 2: Market outcome. The factory produces where its own MPC equals the marginal private benefit (MPB), yielding a market equilibrium quantity Qm at price Pm. This ignores the external cost.
第二步：市场结果。工厂在其MPC等于边际私人收益（MPB）处进行生产，得到市场均衡数量Qm和价格Pm。这忽略了外部成本。
SB (marginal social benefit). Because MSC > MPC, the socially optimal quantity Qs is lower than the free-market quantity Qm. The market is overproducing the good.
第三步：社会最优。社会有效的产出出现在MSC等于边际社会收益（MSB）之处。由于MSC > MPC，社会最优数量Qs低于自由市场数量Qm。市场过度生产了该商品。
Step 4: Welfare loss. The overproduction creates a deadweight welfare loss, represented by the triangle between MSC, MSB, and the quantity axis from Qs to Qm. This is a clear case of market failure requiring government intervention, such as a pollution tax or regulation.
第四步：福利损失。过度生产造成了无谓福利损失，表现为位于MSC、MSB以及从Qs到Qm数量轴之间的三角形区域。这是一个明显的市场失灵案例，需要政府干预，如征收污染税或实施管制。
5. Fiscal Policy Tools: Expansionary vs Contractionary | 财政政策工具：扩张与紧缩
Example: An economy is experiencing a recessionary gap, with high unemployment and low real GDP growth. Explain how the government could use expansionary fiscal policy to close the gap.
例题：某一经济体正在经历衰退缺口，失业率高企，实际GDP增长低迷。解释政府如何利用扩张性财政政策来消除这一缺口。
Step 1: Identify the tools. The government can increase its spending on goods and services (e.g., infrastructure projects) and/or reduce taxes (e.g., income tax cuts). Both actions aim to boost aggregate demand (AD).
第一步：确定工具。政府可以增加商品和服务的支出（例如基础设施项目）和/或减税（例如降低所得税）。这两项措施都旨在提振总需求（AD）。
ases AD (AD = C + I + G + X − M). The AD curve shifts to the right, from AD1 to AD2.
第二步：直接注入。增加政府支出会直接提升AD（AD = C + I + G + X − M）。AD曲线向右移动，从AD1移至AD2。
Step 3: Multiplier effect. Tax cuts raise disposable income, which stimulates consumer spending (C). The initial increase in spending sets off a multiplier process, where the final increase in national income is larger than the initial injection. This further shifts AD to AD3.
第三步：乘数效应。减税提高了可支配收入，刺激了消费支出（C）。初始支出的增加会引发乘数过程，即国民收入的最终增加量大于初始注入量。这会将AD进一步推至AD3。
Step 4: Outcome. Real GDP expands from Y1 towards full-employment level Yf, and unemployment falls. However, if the economy is already near full capacity, expansionary policy risks causing demand-pull inflation instead of real growth, so the position of the AD/AS equilibrium is crucial.
第四步：结果。实际GDP从Y1扩张到接近充分就业水平Yf，失业率下降。然而，如果经济已接近满负荷运转，扩张性政策可能会引发需求拉动型通胀，而非实际增长，因此AD/AS均衡点的位置至关重要。
6. Exchange Rates and the Current Account | 汇率与经常账户
Example: The pound sterling depreciates significantly against the US dollar and the euro. Explain how this depreciation might improve the UK's current account balance, and identify any conditions under which the improvement may not occur.
例题：英镑对美元和欧元大幅贬值。解释这种贬值可能如何改善英国的经常账户余额，并指出在哪些条件下改善可能不会发生。
Step 1: Effect on exports. A weaker pound makes UK exports cheaper in foreign currency terms. This should increase the quantity of exports demanded, assuming demand is price elastic.
第一步：对出口的影响。英镑走弱使英国出口在国际市场上以外币计价变得更便宜。假设需求具有价格弹性，这会增加对出口商品的需求量。
Step 2: Effect on imports. Imports become more expensive in pound terms, which should reduce the quantity of imports demanded. UK consumers switch to domestically produced goods or imported alternatives become pricier.
第二步：对进口的影响。进口商品以英镑计价变得更加昂贵，这应当减少对进口商品的需求量。英国消费者转向国产商品，或者进口替代品价格升高。
Step 3: Net effect on the current account. The value of exports is expected to rise and the value of imports to fall, improving the trade balance. Export revenue increases if the % rise in volume outweighs the fall in unit price.
第三步：对经常账户的净影响。预计出口价值上升而进口价值下降，从而改善贸易收支。如果出口量的百分比增幅超过单位价格的降幅，出口收入将会增加。
Step 4: The J-curve effect. In the short run, the current account may worsen before it improves because existing contracts are fixed and quantities do not adjust immediately. Over time, as volumes respond to price changes, the deficit should shrink, provided the Marshall-Lerner condition holds (sum of PED for exports and imports > 1).
第四步：J曲线效应。在短期内，经常账户可能在改善前先恶化，因为现有合同价格固定，且数量不会立即调整。随着时间的推移，当数量对价格变化做出反应后，赤字应当缩小，前提是马歇尔-勒纳条件成立（出口和进口的需求价格弹性之和大于1）。
7. Supply-Side Policies in Practice | 供给侧政策的实践
Example: The government invests heavily in vocational training programmes and reduces corporation tax. Analyse how these supply-side policies can increase the economy's potential output and reduce inflationary pressures.
例题：政府大力投资职业培训项目并降低公司税。分析这些供给侧政策如何能增加经济的潜在产出并减轻通胀压力。
Step 1: Improving labour productivity. Training raises the skill level of workers, increasing their productivity. This shifts the long-run aggregate supply (LRAS) curve to the right, from LRAS1 to LRAS2, expanding the productive capacity of the economy.
第一步：提高劳动生产率。培训提高了工人的技能水平，从而提高了他们的生产率。这会使长期总供给（LRAS）曲线向右移动，从LRAS1移至LRAS2，扩大了经济的生产能力。
Step 2: Incentives for investment. Lower corporation tax increases post-tax profits, encouraging firms to invest in new capital and technology. Higher investment boosts both short-run and long-run aggregate supply, as it increases the quantity and quality of capital.
第二步：投资激励。降低公司税增加了税后利润，鼓励企业投资于新资本和技术。更高的投资会提升短期和长期总供给，因为它增加了资本的数量和质量。
Step 3: Non-inflationary growth. As LRAS shifts rightward, the economy can produce more goods and services without upward pressure on prices. Even if aggregate demand grows, a larger capacity means inflation is less likely to accelerate. The equilibrium moves to a higher real GDP at a stable price level.
第三步：无通胀增长。随着LRAS向右移动，经济体可以生产更多的商品和服务，而不会对价格产生上升压力。即使总需求增长，更大的生产能力也意味着通胀不太可能加速。均衡点将移至更高实际GDP和稳定物价水平的位置。
Step 4: Time lags. Supply-side policies often take years to take full effect. Training needs time to complete, and investment projects require planning. Nonetheless, they are crucial for long-term sustainable growth and competitiveness.
第四步：时间滞后。供给侧政策往往需要数年才能充分发挥效果。培训需要时间来完成，投资项目需要规划。尽管如此，它们对于长期可持续增长和竞争力至关重要。
8. Market Structure: Monopoly and Efficiency | 市场结构：垄断与效率
Example: A single pharmaceutical company holds a patent for a life-saving drug, making it the only supplier. Explain how this monopoly can lead to allocative and productive inefficiency compared with a perfectly competitive market.
例题：一家制药公司持有某种救命药物的专利，成为唯一供应商。与完全竞争市场相比，解释这种垄断如何导致配置效率和产出效率的损失。
Step 1: Profit maximisation. A monopolist maximises profit by producing the quantity where marginal cost (MC) equals marginal revenue (MR), and then charges the highest price consumers are willing to pay on the demand curve. This yields price Pm and quantity Qm.
第一步：利润最大化。垄断者通过在边际成本（MC）等于边际收益（MR）的产量水平生产来实现利润最大化，然后根据需求曲线收取消费者愿意支付的最高价格。这产生了价格Pm和数量Qm。
Step 2: Allocative inefficiency. In perfect competition, the market equilibrium occurs where price (P) equals MC, reflecting the true cost of resources. The monopolist restricts output and charges a price above MC, so P > MC at Qm. This underproduction means resources are misallocated, and there is a deadweight welfare loss (the triangle of lost consumer and producer surplus).
第二步：配置效率低下。在完全竞争中，市场均衡出现在价格等于边际成本之处，反映了资源的真实成本。而垄断者限制产出，收取高于MC的价格，因此在Qm处P > MC。这种生产不足意味着资源配置不当，并且存在无谓福利损失（即消费者和生产者剩余损失构成的三角形区域）。
Step 3: Productive inefficiency. A monopolist may not have an incentive to minimise average total costs (ATC) because it faces no competitive pressure. In contrast, perfectly competitive firms are forced to produce at the minimum point of the ATC curve in the long run. The monopoly may therefore operate with X-inefficiency, where costs are higher than necessary.
第三步：产出效率低下。垄断者可能没有动力将平均总成本（ATC）降至最低，因为它不会面临竞争压力。相比之下，完全竞争企业在长期中被迫在ATC曲线的最低点进行生产。因此，垄断企业可能存在X-非效率，即成本高于必要水平。
Step 4: Dynamic efficiency caveat. Despite static inefficiencies, a monopoly protected by a patent might have the supernormal profits to invest in research and development, leading to innovation. This dynamic efficiency could benefit consumers in the long term, which is why patents exist; however, the static welfare loss from restricted output must be weighed against these dynamic gains.
第四步：动态效率的补充说明。尽管存在静态无效率，但受专利保护的垄断企业可能拥有超额利润投资于研发，进而带来创新。这种动态效率长期可能使消费者受益，这也是专利制度存在的理由；然而，需要将因限制产量造成的静态福利损失与这些动态收益进行权衡。
Published by TutorHao | Economics Revision Series | aleveler.com
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