📚 IGCSE Economics: Worked Examples Explained | IGCSE 经济：典型例题详解
Economics is not just about memorising definitions; it is about applying concepts to real-world scenarios and interpreting data accurately. In IGCSE Economics, high marks go to students who can break down a question, identify the relevant economic principle, and structure a logical, well-supported answer. This article walks through worked examples spanning demand and supply shifts, elasticity calculations, market failure, macroeconomic indicators, and policy evaluation. Each example mimics the style of Paper 1 multiple‑choice or Paper 2 structured questions, with full explanations that sharpen both analytical skills and exam technique.
经济学不是死记硬背定义，而是要把概念应用到真实场景中并准确解读数据。在IGCSE经济考试中，高分属于那些能拆解题目、锁定相关经济原理、并构建逻辑清晰、论证充分的答案的学生。这篇文章通过典型例题详解，涵盖供需变化、弹性计算、市场失灵、宏观经济指标和政策评估。每个例题都模仿卷一选择题或卷二结构化问答的风格，并配有完整解析，旨在提升分析能力和应试技巧。
1. Demand and Supply Shifts | 需求与供给的移动
In the market for electric scooters, the government introduces a subsidy for manufacturers. At the same time, a health campaign highlights the benefits of outdoor exercise. Analyse the combined effect on the equilibrium price and quantity.
在电动滑板车市场中，政府为制造商提供补贴，同时一项健康宣传活动凸显户外运动的好处。请分析这对均衡价格和数量的综合影响。
A subsidy to producers shifts the supply curve rightwards from S₁ to S₂, because the cost of production falls. The health campaign increases consumer preference for electric scooters, shifting the demand curve rightwards from D₁ to D₂. When both curves shift right, equilibrium quantity unambiguously rises (Q₁ → Q₂). The change in price is indeterminate without knowing the relative magnitudes of the shifts. If the increase in demand outweighs the increase in supply, price rises. If the supply increase is larger, price falls. If they are equal, price remains stable. In an exam, always state that quantity increases but the price effect depends on the relative sizes of the shifts.
对生产者的补贴使供给曲线从S₁右移至S₂，因为生产成本下降。健康宣传活动提高了消费者对电动滑板车的偏好，使需求曲线从D₁右移至D₂。当两条曲线都向右移动时，均衡数量一定增加（Q₁→Q₂）。若不知移动的相对幅度，价格变化无法确定。如果需求增加幅度大于供给增加幅度，价格上升；如果供给增加幅度更大，价格下降；若两者相等，价格保持不变。考试中务必说明数量增加，但价格效应取决于移动的相对大小。
2. Calculating Price Elasticity of Demand (PED) | 需求价格弹性（PED）的计算
A cinema reduces ticket prices from $12 to $10. Weekly ticket sales increase from 500 to 700. Calculate the PED and interpret the result. Should the cinema lower prices further to increase total revenue?
一家影院将票价从12美元降至10美元，每周售票量从500张增至700张。计算PED并解释结果。影院是否应继续降价以增加总收入？
Percentage change in quantity demanded = [(700−500)÷500] × 100 = 40%.
需求量变动的百分比 = [(700−500) ÷ 500] × 100 = 40%。
Percentage change in price = [(10−12)÷12] × 100 = −16.67%.
价格变动的百分比 = [(10−12) ÷ 12] × 100 = −16.67%。
PED = 40% ÷ 16.67% = 2.4 (ignoring the minus sign). PED > 1, so demand is price elastic. When demand is elastic, a price cut raises total revenue because the proportional increase in quantity demanded exceeds the proportional fall in price. Original total revenue = $12 × 500 = $6,000. New total revenue = $10 × 700 = $7,000. Total revenue rises by $1,000. The cinema should consider further price reductions, but only if the demand remains elastic; beyond a certain point PED may fall below 1.
PED = 40% ÷ 16.67% = 2.4（忽略负号）。PED > 1，需求富有弹性。需求富有弹性时，降价会提高总收入，因为需求量增加的百分比大于价格下降的百分比。原总收入 = 12 × 500 = 6,000美元。新总收入 = 10 × 700 = 7,000美元。总收入增加了1,000美元。影院可以考虑进一步降价，但前提是需求仍保持弹性；一旦超过某一点，PED可能降至1以下。
3. Opportunity Cost in Production Possibility Curves | 生产可能性曲线中的机会成本
A country can produce two goods: wheat and steel. Moving from point A to point B on its PPC, wheat output falls by 30 units while steel output rises by 10 units. Calculate the opportunity cost of producing one additional unit of steel in terms of wheat forgone.
一个国家可以生产两种商品：小麦和钢铁。其生产可能性曲线上，从A点移动到B点，小麦产量减少30单位，钢铁产量增加10单位。请计算多生产一单位钢铁的机会成本，以放弃的小麦数量表示。
Opportunity cost = Quantity of wheat sacrificed ÷ Quantity of steel gained = 30 wheat ÷ 10 steel = 3 wheat per 1 steel. This means that for every additional unit of steel produced, the economy must give up 3 units of wheat. The opportunity cost is constant if the PPC is a straight line, or increasing if the PPC is concave to the origin. In this example, the calculated ratio represents the marginal rate of transformation between the two goods.
机会成本 = 放弃的小麦数量 ÷ 获得的钢铁数量 = 30 ÷ 10 = 3单位小麦/1单位钢铁。这意味着每多生产一单位钢铁，经济必须放弃3单位小麦。若PPC为直线，机会成本不变；若PPC凹向原点，机会成本递增。本例中计算出的比率代表两种商品之间的边际转换率。
4. Market Failure and Externalities | 市场失灵与外部性
Explain how a tax on sugary drinks can correct a negative externality. Use a diagram in your explanation.
解释对含糖饮料征税如何纠正负外部性。请用图表辅助说明。
Sugary drinks generate negative externalities in consumption: consumers do not bear the full healthcare costs, obesity-related productivity losses, and public health burdens. The marginal private benefit (MPB) exceeds the marginal social benefit (MSB). In a free market, the equilibrium quantity is Qp, where MPB = MPC (marginal private cost). The socially optimal quantity is Qs, where MSB = MSC. Because the market overconsumes, there is a welfare loss (deadweight loss triangle between Qs and Qp). A tax equal to the external cost per unit shifts the supply curve upward by the tax amount, raising the price to consumers. This reduces the quantity demanded towards Qs, internalising the externality. The tax revenue can fund healthcare or education campaigns, further reducing the externality.
含糖饮料在消费中产生负外部性：消费者未承担全部医疗成本、肥胖相关的生产力损失和公共健康负担。边际私人收益（MPB）大于边际社会收益（MSB）。自由市场中，均衡数量为Qp，即MPB = MPC（边际私人成本）处。社会最优数量为Qs，即MSB = MSC处。由于市场过度消费，产生了福利损失（Qs和Qp之间的无谓损失三角形）。征收等于每单位外部成本的税收，使供给曲线向上移动税额幅度，提高消费者支付的价格。这将需求量降至接近Qs，内部化外部性。税收收入可用于资助医疗或教育宣传，进一步减少外部性。
5. Exchange Rates: Appreciation and Depreciation | 汇率：升值和贬值
The UK pound depreciates by 15% against the US dollar. Analyse how this affects a UK firm that imports raw materials from the US and exports finished goods to the US.
英镑对美元贬值15%。分析这对一家从美国进口原材料并向美国出口成品的英国企业有何影响。
A weaker pound means each pound buys fewer dollars. For the UK importer, the cost of US raw materials in pounds rises, increasing production costs. This squeezes profit margins unless the firm can absorb the higher costs or pass them on. However, the same depreciation makes the firm’s exports cheaper in dollar terms, raising the price competitiveness of its finished goods in the US market. The net effect depends on the relative proportions of imported inputs and exported output. If the firm’s exports are highly price elastic, the volume increase may offset the higher import costs. This is an application of the Marshall‑Lerner condition in a microeconomic setting. The firm may hedge exchange rate risk or source materials locally to reduce exposure.
英镑走弱意味着每英镑能兑换的美元减少。对英国进口商而言，以英镑计价的美国原材料成本上升，增加了生产成本。除非企业能消化或转嫁更高的成本，否则利润率会受挤压。但同一贬值使企业的出口商品以美元计价变得更便宜，提升了其成品在美国市场的价格竞争力。净效应取决于进口投入和出口产出的相对比例。若企业出口商品的需求价格弹性很高，销售量增加可能抵消进口成本上升。这是马歇尔‑勒纳条件在微观层面的应用。企业可通过汇率风险对冲或本地采购原材料来降低风险敞口。
6. Inflation and the Consumer Price Index (CPI) | 通货膨胀与消费者价格指数 (CPI)
A typical consumer basket contains 40 units of housing, 30 units of food, and 30 units of entertainment. Base‑year prices are: housing $10/unit, food $5/unit, entertainment $8/unit. Current‑year prices are: housing $12/unit, food $6/unit, entertainment $9/unit. Calculate the CPI and the rate of inflation.
一个典型消费者篮子包含40单位住房、30单位食品和30单位娱乐。基年价格为：住房每单位10美元，食品每单位5美元，娱乐每单位8美元。当年价格为：住房每单位12美元，食品每单位6美元，娱乐每单位9美元。计算CPI和通货膨胀率。
| Category | Base‑year cost | Current‑year cost |
| Housing | 40 × $10 = $400 | 40 × $12 = $480 |
| Food | 30 × $5 = $150 | 30 × $6 = $180 |
| Entertainment | 30 × $8 = $240 | 30 × $9 = $270 |
| Total basket cost | $790 | $930 |
CPI = (Cost in current year ÷ Cost in base year) × 100 = ($930 ÷ $790) × 100 = 117.72.
CPI = （当年成本 ÷ 基年成本）× 100 = （930 ÷ 790）× 100 = 117.72。
Inflation rate = (CPI current − CPI base) ÷ CPI base × 100 = (117.72 − 100) ÷ 100 × 100 = 17.72%.
通货膨胀率 = （当年CPI − 基年CPI）÷ 基年CPI × 100 = （117.72 − 100）÷ 100 × 100 = 17.72%。
This simplified method assumes the same weights and basket composition. In reality, CPI calculations use larger baskets and updated weights. A rising CPI reduces real incomes if nominal incomes stay constant, and it erodes the purchasing power of savings.
该简化方法假设权重和篮子构成不变。实际CPI计算会使用更大的篮子和更新的权重。CPI上升若名义收入保持不变，会降低实际收入，并侵蚀储蓄的购买力。
7. Unemployment Types and Measurement | 失业类型与衡量
A coal mine closes due to a government ban on coal‑fired power stations. The laid‑off miners are looking for jobs in the renewable energy sector but lack the necessary skills. Identify the type of unemployment and suggest a policy solution.
一家煤矿因政府禁止燃煤发电站而关闭。被裁员的矿工正在可再生能源行业寻找工作，但缺乏必要技能。指出失业类型并提出政策解决方案。
This is structural unemployment: a mismatch between the skills of workers and the requirements of new jobs, often caused by long‑term changes in the structure of the economy. The decline of coal mining and the growth of green energy is a classic example. Frictional unemployment would be temporary and voluntary, such as a worker moving between jobs; cyclical unemployment would result from a lack of aggregate demand in a recession. Structural unemployment persists even when the economy is growing. A suitable policy is government‑funded retraining programmes that equip miners with skills in solar panel installation, wind turbine maintenance, or battery technology. Subsidised apprenticeships and relocation allowances can also improve geographic mobility. Without intervention, structural unemployment reduces the economy’s productive capacity and increases long‑term inequality.
这是结构性失业：工人技能与新工作要求不匹配，通常由经济结构的长期变化引起。煤炭开采衰落与绿色能源兴起是经典例子。摩擦性失业是暂时的、自愿的，如工人换工作时期；周期性失业则源于经济衰退导致的总需求不足。结构性失业即使在经济上升期也会持续。合适的政策是政府出资的再培训计划，使矿工掌握太阳能板安装、风力涡轮维护或电池技术等技能。补贴学徒计划和搬迁津贴也能提高地域流动性。若无干预，结构性失业将降低经济的生产能力并加剧长期不平等。
8. Labour Market and Minimum Wage | 劳动力市场与最低工资
A government raises the national minimum wage by 25%. Discuss the possible effects on employment, consumer prices, and income inequality.
政府将全国最低工资提高25%。讨论这对就业、消费者价格和收入不平等的可能影响。
A higher minimum wage acts as a price floor in the labour market. If set above the equilibrium wage, it can create a surplus of labour (classical unemployment) because firms demand fewer workers at a higher wage. The extent of job losses depends on the wage elasticity of labour demand. In industries with inelastic demand for labour, employment may fall only slightly. However, firms may respond by raising prices to maintain profit margins, contributing to cost‑push inflation. On the positive side, a minimum wage hike directly boosts the earnings of low‑paid workers, compressing the wage distribution and reducing income inequality. Some workers may see higher disposable income, which stimulates consumption. Others argue that higher pay improves productivity and reduces staff turnover, partly offsetting the cost increase. The overall outcome depends on the initial wage level, the economy’s institutional framework, and the rate at which the minimum wage is adjusted relative to average earnings.
更高的最低工资在劳动力市场中充当价格下限。若设在均衡工资之上，可能造成劳动力过剩（古典失业），因为企业在更高工资下需要的工人减少。失业程度取决于劳动力需求的工资弹性。在劳动力需求缺乏弹性的行业，就业下降的幅度可能很小。但企业可能通过提高价格来维持利润率，导致成本推动型通胀。从积极方面看，最低工资上调直接增加低薪工人的收入，压缩工资分配并减少收入不平等。部分工人的可支配收入提高，刺激消费。另有观点认为高收入能提高生产率并降低员工流失率，部分抵消成本增加。总体结果取决于初始工资水平、经济的制度框架以及最低工资相对于平均收入的调整速度。
9. Monetary Policy Tools | 货币政策工具
An economy faces inflation of 8%, above the 2% target. The central bank decides to raise the base interest rate. Explain the transmission mechanism through which this reduces inflation.
一经济体面临8%的通货膨胀，高于2%的目标。中央银行决定提高基准利率。解释其降低通胀的传导机制。
A higher base rate raises the cost of borrowing and increases the return on saving. Commercial banks pass on the higher rate to consumers and firms through more expensive mortgages, loans, and overdrafts. This reduces consumption of durable goods and investment spending because households and firms cut interest‑sensitive expenditure. At the same time, existing borrowers with variable‑rate debt have less disposable income, further dampening demand. Higher saving returns encourage more saving and less spending. All these factors reduce aggregate demand (AD shifts left). As demand falls, firms face downward pressure on prices, and inflation gradually slows. The exchange rate channel also operates: higher interest rates attract foreign capital inflows, appreciating the currency, which reduces import prices (disinflationary effect). The strength of the transmission mechanism depends on the responsiveness of consumers and firms to rate changes, the share of variable‑rate debt, and the openness of the economy.
基准利率上调提高了借款成本并增加储蓄回报。商业银行通过更高的抵押贷款、贷款和透支利率将上调传递给消费者和企业。这减少了耐用品消费和投资支出，因为家庭和企业削减了对利率敏感的开支。同时，持有浮动利率债务的现有借款人可支配收入减少，进一步抑制需求。更高的储蓄回报鼓励更多储蓄、减少支出。所有这些因素降低了总需求（AD左移）。随着需求下降，企业面临降价压力，通胀逐渐放缓。汇率渠道也在起作用：更高利率吸引外资流入，推动本币升值，从而降低进口价格（通缩效应）。传导机制的效力取决于消费者和企业对利率变动的反应程度、浮动利率债务的占比以及经济的开放度。
10. Fiscal Policy and Multiplier Effect | 财政政策与乘数效应
A government increases infrastructure spending by $5 billion. The marginal propensity to consume (MPC) is 0.8. Calculate the simple multiplier and the total increase in GDP. Explain why the actual multiplier might be smaller.
政府增加基础设施支出50亿美元。边际消费倾向（MPC）为0.8。计算简单乘数和GDP的总增加量。说明实际乘数为何可能更小。
Simple multiplier k = 1 ÷ (1 − MPC) = 1 ÷ (1 − 0.8) = 1 ÷ 0.2 = 5.
简单乘数 k = 1 ÷ (1 − MPC) = 1 ÷ (1 − 0.8) = 1 ÷ 0.2 = 5。
Total increase in GDP = Initial injection × k = $5 billion × 5 = $25 billion.
GDP总增加量 = 初始注入 × k = 50亿美元 × 5 = 250亿美元。
In reality, the multiplier is often smaller because of leakages: some of the additional income is saved (already accounted for, but marginal propensity to save may be higher than 0.2 if confidence is low); some is spent on imports (marginal propensity to import, mpm > 0), which does not generate domestic production; and some may be paid as taxes (marginal tax rate, mtr > 0), reducing disposable income available for consumption. Supply‑side constraints such as skill shortages or lack of capital may also prevent output from expanding fully. Finally, crowding out can occur if government borrowing raises interest rates and reduces private investment. A more realistic multiplier incorporating taxes and imports is k = 1 ÷ (1 − MPC(1 − mtr) + mpm).
现实中乘数往往更小，因为有漏出：部分额外收入被储蓄（已计入，但若信心不足，边际储蓄倾向可能高于0.2）；部分用于购买进口品（边际进口倾向mpm > 0），不形成国内产出；部分作为税收支付（边际税率mtr > 0），减少可用于消费的可支配收入。技能短缺或资本不足等供给侧制约也可能阻碍产出完全扩张。最后，如果政府借款推高利率并挤出私人投资，会发生挤出效应。纳入税收和进口的更现实乘数为 k = 1 ÷ (1 − MPC(1 − mtr) + mpm)。
11. Comparative Advantage and Trade | 比较优势与贸易
Country X produces 100 units of cloth or 50 units of wine per worker per day. Country Y produces 80 units of cloth or 20 units of wine. Determine comparative advantage and the range of mutually beneficial terms of trade.
X国每个工人每天能生产100单位布料或50单位葡萄酒。Y国每个工人每天能生产80单位布料或20单位葡萄酒。确定比较优势和双方互利的贸易条件范围。
| Cloth per worker | Wine per worker | Opportunity cost of 1 cloth | Opportunity cost of 1 wine | |
| Country X | 100 | 50 | 0.5 wine | 2 cloth |
| Country Y | 80 | 20 | 0.25 wine | 4 cloth |
Country Y has a lower opportunity cost in cloth (0.25 wine < 0.5 wine), so Y has a comparative advantage in cloth. Country X has a lower opportunity cost in wine (2 cloth < 4 cloth), so X has a comparative advantage in wine. Both countries benefit from trade if the terms of trade lie between their domestic opportunity costs. For cloth, export from Y must fetch between 0.25 and 0.5 wine per cloth. For wine, export from X must fetch between 2 and 4 cloth per wine. A possible mutually beneficial term is 1 cloth = 0.4 wine (or 1 wine = 2.5 cloth). By specialising and trading, both countries can consume beyond their individual PPCs.
Y国在生产布料上的机会成本更低（0.25葡萄酒 < 0.5葡萄酒），故Y在布料上具有比较优势。X国在生产葡萄酒上的机会成本更低（2布料 < 4布料），故X在葡萄酒上具有比较优势。如果贸易条件位于两国国内机会成本之间，两国都能从贸易中获益。Y的布料出口，每单位布料须换得0.25至0.5单位葡萄酒。X的葡萄酒出口，每单位葡萄酒须换得2至4单位布料。一个可能的互利条件是1布料 = 0.4葡萄酒（或1葡萄酒 = 2.5布料）。通过专业化分工和贸易，两国都能消费超过各自生产可能性曲线之外的商品组合。
12. Economic Growth and Sustainable Development | 经济增长与可持续发展
Explain the difference between actual and potential economic growth. Using a PPC or AD/AS diagram, illustrate how investment in human capital can achieve sustainable long‑term growth.
解释实际经济增长与潜在经济增长的区别。使用PPC或AD/AS图，说明人力资本投资如何实现可持续的长期增长。
Actual economic growth is the percentage increase in real GDP over a period, reflecting short‑term demand‑side fluctuations. Potential economic growth is the increase in the economy’s productive capacity, shown by an outward shift of the PPC or the long‑run aggregate supply (LRAS) curve. Investment in human capital — education, training, and healthcare — raises labour productivity and the quality of the workforce. In the production possibility curve model, this shifts the entire curve outward, allowing a greater combination of goods to be produced. In the AD/AS model, it shifts the LRAS curve to the right. Sustainable growth requires that the increase in productive capacity does not deplete natural resources or cause irreversible environmental damage. For example, investing in green technology skills ensures that growth today does not compromise future generations’ well‑being. Governments can support human capital development through publicly funded schools, vocational programmes, and healthcare provision, though there is an opportunity cost in terms of current consumption.
实际经济增长是指一段时期内实际GDP的百分比增长，反映短期的需求侧波动。潜在经济增长是经济生产能力的提高，表现为PPC或长期总供给（LRAS）曲线向外移动。人力资本投资——教育、培训和医疗——提高了劳动生产率和劳动力素质。在生产可能性曲线模型中，这使整条曲线向外平移，能够实现更多商品组合。在AD/AS模型中，它使LRAS曲线右移。可持续增长要求生产能力的扩大不能耗尽自然资源或造成不可逆的环境破坏。例如，投资于绿色技术技能可以确保今天的发展不损害后代的福祉。政府可通过公立学校、职业培训和公共医疗来支持人力资本发展，尽管这存在以牺牲当前消费为代价的机会成本。
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