📚 IB & WJEC Economics: Typical Exam Question Walkthrough | IB WJEC 经济：典型例题详解
This article works through a selection of classic exam-style questions that regularly appear in IB and WJEC Economics papers. Each worked example explains the key concepts, calculation steps and evaluation points you need to score top marks.
本文精选了 IB 与 WJEC 经济考试中反复出现的经典例题，逐一详解核心概念、计算步骤与评估要点，助你稳稳拿分。
1. Shifts in Demand and Supply | 需求与供给的移动
A common short-answer question provides a scenario such as: ‘The government introduces a subsidy for solar panel producers. Illustrate and explain the effect on the solar panel market.’
一道常见的简答题会给出如下情境：“政府为太阳能板生产商提供补贴。请作图并解释对太阳能板市场的影响。”这类题目要求准确区分是需求还是供给曲线发生移动。
The subsidy lowers production costs, so the supply curve shifts right (S₁ → S₂). This creates a new equilibrium with a lower market price P₂ and a higher quantity Q₂. Students must show correct axis labels (Price, Quantity), a clear rightward supply shift, and a properly labelled new equilibrium. In a WJEC context, the diagram alone may carry 3-4 marks out of 6.
补贴降低了生产成本，因此供给曲线向右移动（S₁ → S₂），形成新的均衡——市场价格降至 P₂，交易量增至 Q₂。答题时必须正确标注坐标轴（价格、数量），清晰画出右移的供给曲线并标出新均衡点。在 WJEC 考试中，仅作图就占到 3-4 分（满分 6 分）。
For higher-band marks in IB, add an evaluative point: the subsidy’s actual impact depends on price elasticity of demand. With inelastic demand, the price fall is larger but the quantity increase is modest, limiting the environmental benefit.
若想冲击 IB 高分段，还需补充评估：补贴的实际效果取决于需求价格弹性。若需求缺乏弹性，价格降幅更大，但数量增幅有限，环境改善效果可能会打折扣。
2. Calculating Price Elasticity of Demand (PED) | 需求价格弹性计算
A typical numerical question: ‘A cinema raises ticket price from £8 to £10, and daily customers fall from 400 to 320. Calculate and interpret the PED.’
典型计算题：“电影院将票价从 8 英镑上调至 10 英镑，每日观影人数从 400 人降至 320 人。计算并解释需求价格弹性。”
First, find percentage changes using the midpoint method or simple percentage. Midpoint: %ΔQ = (320-400)/((400+320)/2) × 100 = -80/360 × 100 ≈ -22.2%. %ΔP = (10-8)/((8+10)/2) × 100 = 2/9 × 100 ≈ 22.2%.
先用中点法求百分比变化。%ΔQ = (320-400)/[(400+320)/2] × 100 = -80/360 × 100 ≈ -22.2%。%ΔP = (10-8)/[(8+10)/2] × 100 = 2/9 × 100 ≈ 22.2%。
PED = %ΔQd / %ΔP = -22.2% / 22.2% = -1.0
PED = -1.0, meaning unit elastic demand. Total revenue before is 8×400=£3,200; after is 10×320=£3,200. Revenue unchanged – exactly what unit elasticity predicts. WJEC mark schemes reward correct formula, calculation and comment on revenue.
PED 为 -1.0，即单位弹性。提价前总收入为 8×400=3200 英镑，提价后为 10×320=3200 英镑，总收入不变，完全符合单位弹性的预测。WJEC 评分标准看重公式、计算过程及对收入的点评。
3. Price Controls: Maximum Price (Ceiling) | 最高限价
Draw and analyse a maximum price set below equilibrium, e.g., a rent control at Pmax for apartments. The quantity supplied falls to Qs, quantity demanded rises to Qd, creating a persistent shortage (Qd – Qs).
画出低于均衡价的最高限价，如对公寓实施租金管制 Pmax。此时供给量缩减至 Qs，需求量增至 Qd，形成持续短缺（Qd – Qs）。
Key marks: correct binding position, labelling shortage, shading or indicating welfare loss (deadweight loss). In IB Paper 1, explain that while it makes housing more affordable for those who find a flat, the shortage leads to black markets, queues and reduced maintenance. WJEC often asks for an EVALUATION: a maximum price may be justified if the good has positive externalities (e.g., merit good argument).
得分关键：限价位于有效位置，标出短缺，可额外标明无谓损失。IB 卷一要求解释：限价虽让租到房的人更易负担，但短缺会催生黑市、排队现象及房屋维修减少。WJEC 常要求评估：若商品具有正外部性（如优效品），最高限价或许存在合理依据。
4. Indirect Tax Incidence | 间接税的税收归宿
‘A £3 specific tax is placed on cigarettes. The pre-tax equilibrium is P=£10, Q=100k packs. After tax, consumers pay £12.50 and producers receive £9.50. Calculate tax burden per side.’
“对香烟征收每包 3 英镑的从量税。税前均衡为 P=10 英镑，Q=10 万包。税后消费者支付 12.50 英镑，生产者实收 9.50 英镑。计算双方的税负。”
Consumer burden = £12.50 – £10 = £2.50 per unit. Producer burden = £10 – £9.50 = £0.50 per unit. Total tax = £3. Diagrammatically, this occurs because demand for cigarettes is inelastic relative to supply – consumers bear a larger share.
消费者负担 = 12.50 – 10 = 2.50 英镑/包；生产者负担 = 10 – 9.50 = 0.50 英镑/包。总税额 3 英镑。图形上，这是因为香烟需求相对供给更加缺乏弹性，消费者不得不承担更多税负。
IB mark schemes expect you to link the split to relative elasticities explicitly. Add a real-world insight: governments often tax addictive goods both for revenue and to reduce consumption – the size of the quantity drop depends on PED.
IB 评分标准要求明确将税负分担与相对弹性挂钩。可补充现实视角：政府对成瘾品征税，既为财政收入也为抑制消费——消费量的降幅大小则取决于需求价格弹性。
5. Negative Externality of Production | 生产的负外部性
Examine a coal-fired power plant emitting pollution. The marginal private cost (MPC) lies below marginal social cost (MSC). Free-market output is Qmarket where MPB = MPC, but social optimum is Qsocial where MSB = MSC.
以排放污染的燃煤电厂为例。边际私人成本（MPC）低于边际社会成本（MSC）。自由市场产出在 MPB=MPC 处，即 Qmarket；社会最优产出在 MSB=MSC 处，即 Qsocial。
Draw MSC above MPC by the external cost. The overproduction distance (Qmarket – Qsocial) generates welfare loss (shaded triangle). To fix this, a Pigouvian tax equal to the external cost at Qsocial internalises the externality. In WJEC answers, name the triangle as deadweight loss and explicitly state ‘overproduction due to unpriced external costs’.
作图时让 MSC 高于 MPC，高出部分为外部成本。过度生产区间（Qmarket – Qsocial）形成福利损失（阴影三角形）。解决办法是征收等于社会最优处外部成本的庇古税，以内部化外部性。WJEC 作答中应明确称该三角形为无谓损失，并点明“外部成本未被定价导致过度生产”。
Evaluation for IB: taxes are hard to set at the exact damage value; pollution crosses borders, requiring international cooperation; alternative policies like tradable permits may be more efficient long-term.
IB 评估点：征税额度难以精确等于损害值；污染具有跨国性，需国际合作；可交易的排放许可证等替代政策长期可能更有效。
6. Public Goods and Free-Rider Problem | 公共物品与搭便车问题
Define a pure public good (non-rival, non-excludable) using flood defences as an example. Explain why private firms under-provide such goods.
以防洪工程为例定义纯公共物品（非竞争性、非排他性），并解释为何私人企业会供给不足。
Because no one can be excluded once the defence is built, individuals have no incentive to pay – they free-ride. Thus, market demand is virtually zero at any positive price. This causes a missing market. WJEC 6-mark questions often require a diagram with a vertical marginal social benefit (MSB) curve, and a supply (MSC) curve, illustrating optimal quantity Q* where MSB = MSC, but no private provision.
由于防洪设施一旦建成便无法排除任何人使用，个体缺乏付费动机，均想搭便车。因此，在任何正价格上市场需求几乎为零，导致市场缺失。WJEC 的 6 分题通常要求画出垂直的边际社会收益（MSB）曲线和供给（MSC）曲线，指出社会最优数量为 Q*，但私人市场不会提供。
IB students should evaluate by noting that government provision themselves may suffer from inefficiency; public-private partnerships or community action can sometimes overcome the free-rider issue, though rarely for pure public goods.
IB 学生需评估：政府直接提供也可能效率低下；公私合作或社区行动有时能缓解搭便车难题，但纯公共物品极少如此。
7. Aggregate Demand Components and Multiplier | 总需求构成与乘数
Consider a numerical scenario: ‘If marginal propensity to consume (MPC) is 0.75, calculate the spending multiplier. An initial increase in government spending of £20bn will raise real GDP by how much?’
数值情境题：“若边际消费倾向（MPC）为 0.75，计算支出乘数。政府支出最初增加 200 亿英镑，实际 GDP 最终增加多少？”
Multiplier k = 1 / (1 – MPC) = 1 / 0.25 = 4
乘数 k = 1 / (1–MPC) = 1/0.25 = 4。那么，ΔGDP = k × ΔG = 4 × £20bn = £80bn。
Many WJEC candidates forget to explain the process: the initial spending creates income for others who spend 0.75 of it, and so on, generating rounds of induced spending. IB Paper 2 expects you to also discuss the limitations: the multiplier is smaller in an open economy due to leakages (imports, taxes, savings); supply constraints may cause inflation before the full multiplier effect is realised.
许多 WJEC 考生会忘记解释过程：初始支出成为他人收入，后者将其中的 0.75 花掉，如此循环产生引致支出。IB 卷二还要求讨论局限：开放经济中因进口、税收、储蓄等漏出，乘数会变小；供给瓶颈可能使物价上升，乘数效应未完全释放便引发通胀。
8. Fiscal Policy Diagram (Expansionary) | 扩张性财政政策图形
Using AD/AS diagram, show an increase in government spending (or tax cut) shifting AD right from AD₁ to AD₂. Real GDP rises from Y₁ to Y₂, and price level from P₁ to P₂.
用 AD/AS 模型绘出政府支出增加（或减税）使 AD 从 AD₁ 右移至 AD₂。实际 GDP 由 Y₁ 增至 Y₂，物价水平从 P₁ 升至 P₂。
Full marks require correct axis labels (Real GDP, Average Price Level), distinct AD shifts, and an indication that the effect on real output depends on the shape of AS curve. On the flat/Keynesian segment, output rises without much inflation; on the vertical/classical segment, only inflation occurs.
满分作图要求轴标签正确（实际 GDP、平均物价水平），AD 明显移动，并体现对实际产出的影响取决于 AS 曲线形状。在水平（凯恩斯）区间，产出增加而通胀微弱；在垂直（古典）区间，仅物价上升。
IB essays often ask to evaluate crowding out: increased government borrowing may raise interest rates, reducing private investment and dampening the initial expansion. WJEC synoptic questions also link to supply‑side policies for long‑term sustainability.
IB 论文常要求评估挤出效应：政府增加借款可能抬高利率，挤出私人投资，削弱初始扩张。WJEC 的综合题还会关联供给侧政策，以保障长期可持续性。
9. Monetary Policy Transmission Mechanism | 货币政策传导机制
Explain how a central bank lowering the policy rate increases aggregate demand. Start: lower interest rate → cheaper borrowing + lower mortgage payments → households’ and firms’ cashflow improves → consumption (C) and investment (I) rise → AD rises.
解释央行降低政策利率如何增加总需求：降息 → 借款成本降低 + 房贷还款减少 → 家庭和企业现金流改善 → 消费（C）与投资（I）增加 → AD 上升。
Add the exchange rate channel for WJEC: lower interest rates reduce hot money inflows, depreciating the currency. Exports become cheaper, imports dearer, so net exports (X-M) rise, further shifting AD right. Diagrams could include a money market showing an increased money supply, falling interest rate.
WJEC 额外补充汇率渠道：利率降低后热钱流入减少，本币贬值。出口变便宜、进口变贵，净出口 (X-M) 增加，进一步右移 AD。可选图形包括货币市场上货币供给扩大、利率下降。
IB Part (b): evaluate effectiveness when interest rates are near zero (liquidity trap); also, time lags mean the full impact may take 12-18 months, complicating stabilisation policy.
IB 的 b 部分评估：当利率接近零时（流动性陷阱）效力减弱；且时滞效应使全部影响需 12–18 个月才能显现，增大稳定化政策的难度。
10. Comparative Advantage and Terms of Trade | 比较优势与贸易条件
Given output per worker: Country A produces 20 wheat or 10 cloth; Country B produces 15 wheat or 5 cloth. Determine who has comparative advantage in each good.
给定每工人产出：A 国可生产 20 单位小麦或 10 单位布；B 国可生产 15 单位小麦或 5 单位布。判断各自比较优势。
Opportunity cost of 1 wheat: A = 10/20 = 0.5 cloth; B = 5/15 ≈ 0.33 cloth. B has lower opportunity cost in wheat → B has comparative advantage in wheat. A has lower opportunity cost in cloth (2 vs 3 wheat) → A has comparative advantage in cloth. Trade can be mutually beneficial if the terms of trade lie between the two opportunity cost ratios: here 1 wheat should trade for between 0.33 and 0.5 cloth.
1 单位小麦的机会成本：A 为 10/20 = 0.5 单位布；B 为 5/15 ≈ 0.33 单位布。B 国小麦机会成本更低，故 B 在小麦上具有比较优势。A 在布上的机会成本更低（2 < 3 单位小麦），故 A 在布上具有比较优势。若贸易条件落在两国机会成本比之间（此处 1 单位小麦应交换 0.33 至 0.5 单位布），双方均可获益。
IB examiners expect a numerical example showing gains: before trade, A consumes 10 wheat & 5 cloth (half of each). After specialisation and trade, consumption can exceed these bounds. Mention restrictions: transport costs, imperfect competition may erode benefits.
IB 考官希望看到用数字例证贸易收益：贸易前 A 消费 10 小麦与 5 布（各一半），专业化与贸易后消费组合可超出原有边界。补充限制条件：运输成本、不完全竞争等因素可能侵蚀利得。
11. Exchange Rate Determination (Floating) | 浮动汇率决定
Draw a foreign exchange market for sterling (£). Demand comes from exports, FDI; supply from imports, capital outflows. When UK exports increase, demand for £ shifts right, causing appreciation: e₁ → e₂.
画出英镑外汇市场。需求来自出口、外商直接投资；供给源于进口、资本外流。若英国出口增加，英镑需求右移，导致升值：e₁ → e₂。
WJEC data-response often asks to calculate the new value: if initial rate is £1 = $1.30 and pound appreciates by 4%, new rate is $1.30 × 1.04 = $1.352. IB asks to evaluate consequences: appreciation hurts export competitiveness but reduces imported inflation – good for consumers, tough for exporters.
WJEC 数据回应题常要求计算新汇率：若初值 £1 = $1.30，英镑升值 4%，新汇率为 $1.30 × 1.04 = $1.352。IB 要求评估后果：升值削弱出口竞争力，但能降低输入型通胀——对消费者好，对出口商难。
Mention that in speculative markets, ‘hot money’ flows can overwhelm trade flows, making currencies volatile. Central banks may intervene with foreign exchange reserves to manage excessive fluctuations, a topic commonly examined in both syllabuses.
还需提及：在投机市场里，“热钱”流动可能压过贸易流动，导致汇率大幅波动。央行可用外汇储备干预，管理过度波动，这是两个课程都会考查的话题。
12. Evaluating Macro Policy Conflicts | 宏观政策目标的冲突
One frequently examined essay asks: ‘Discuss the potential conflicts between economic growth and a country’s environmental sustainability.’ Or, ‘Can low unemployment coexist with low inflation?’
常考论述题：“讨论经济增长与一国环境可持续性之间的潜在冲突。”或“低失业能与低通胀共存吗？”
A structured answer: Define growth (increase in real GDP) and environmental goals (reducing carbon emissions). Use a production possibility frontier (PPF) diagram to show a bias towards capital goods may cause more pollution. Or an AD/AS diagram showing growth might close a deflationary gap but raise pollution. Conflicts arise because production technologies often rely on fossil fuels; in the short run, there is a trade-off (Phillips curve).
结构化作答：先定义增长（实际 GDP 增加）与环境目标（碳排放减少）。用生产可能性边界（PPF）图展示偏向资本品或导致更多污染；或 AD/AS 图显示增长在消除通缩缺口时可能推高污染。冲突源于现有生产技术多依赖化石燃料；短期内存在权衡（菲利普斯曲线）。
For high marks, discuss win-win scenarios: green growth, circular economy, technological advances in renewables can decouple growth from emissions. Governments can use carbon taxes and subsidies for clean tech. IB Paper 1 requires real-world examples such as Germany’s Energiewende or Costa Rica’s carbon neutrality programme.
为获高分，要讨论双赢局面：绿色增长、循环经济、可再生能源技术进步可使增长与排放脱钩。政府可运用碳税与清洁技术补贴。IB 卷一需要真实案例，如德国的能源转型或哥斯达黎加的碳中和计划。
Published by TutorHao | Economics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导