📚 IB Economics: Worked Examples & Detailed Explanations | IB 经济：典型例题详解
IB Economics papers combine knowledge, application, and analysis in a way that demands practice with real exam-style questions. This article walks you through carefully selected typical questions, showing exactly how to structure answers, apply economic theory, use diagrams, and earn high marks. Each example is broken down step by step in both English and Chinese to help you master the technique.
IB 经济考试将知识、应用与分析融为一体，需要通过真实考题进行反复练习。本文精选典型例题，一步步展示如何组织答案、运用经济理论、画图并夺取高分。每个例子都以中英对照方式分解，帮助你掌握技巧。
1. Understanding Command Terms | 理解指令词
IB exam questions use specific command terms that tell you exactly what to do. Misreading them is a common reason for losing marks.
IB 考试题目使用特定的指令词，精确告诉你该做什么。误解它们往往是失分的常见原因。
“Explain” requires a detailed account of how something works, supported by a diagram and real-world mechanism. “Analyse” breaks down a situation into parts and shows the connections. “Evaluate” demands a balanced discussion, weighing advantages and disadvantages, considering stakeholders, and reaching a supported judgment. “Discuss” is similar but often allows broader exploration. Always underline the command term in the question.
“解释”要求详细说明某事物的运作方式，并附以图表和现实机制。“分析”将情况分解成部分，揭示其内在联系。“评价”则需要进行平衡的讨论，权衡利弊，考虑利益相关者，并得出有依据的判断。“讨论”类似但允许更广泛的探索。务必在题目中划出指令词。
For a 10-mark “Explain” question, spend about 20 minutes and focus on theory and diagram. For a 15-mark “Evaluate”, allocate 30 minutes and ensure you offer a clear conclusion.
对于10分的“解释”题，花约20分钟，专注于理论和图表。对于15分的“评价”题，分配30分钟，确保给出明确的结论。
2. Example 1: Market Equilibrium Change (Paper 1, 10 marks) | 例题1：市场均衡变化（试卷一，10分）
Question: “Explain how a successful advertising campaign by electric scooter manufacturers will affect the market equilibrium for electric scooters.”
题目：“解释电动滑板车制造商成功的广告宣传活动将如何影响电动滑板车的市场均衡。”
Start by drawing a standard supply and demand diagram. Label the vertical axis ‘Price’ and the horizontal axis ‘Quantity’. Show an initial equilibrium at P1, Q1.
首先画出标准的供需图。纵轴标为“价格”，横轴标为“数量”。在 P1、Q1 处标出初始均衡点。
A successful advertising campaign increases consumer preferences, shifting the demand curve to the right from D1 to D2. Supply remains unchanged initially.
成功的广告活动增强了消费者偏好，需求曲线从 D1 向右移动至 D2。供给最初保持不变。
At the original price P1, there is now excess demand (a shortage). This puts upward pressure on price. As price rises, quantity supplied expands along the supply curve and quantity demanded contracts along the new demand curve until a new equilibrium is reached at a higher price P2 and higher quantity Q2.
在原价格 P1 下，出现超额需求（短缺），从而推动价格上升。随着价格上升，供给量沿供给曲线增加，需求量沿新需求曲线收缩，直到在更高的价格 P2 和更高的数量 Q2 处形成新的均衡。
Thus, the market experiences a higher equilibrium price and a higher equilibrium quantity. The diagram clearly illustrates the rightward demand shift and the movement along the supply curve.
因此，市场获得更高的均衡价格和更高的均衡数量。该图清晰地展示了需求右移以及沿着供给曲线的移动。
3. Example 2: Evaluating a Price Ceiling (Paper 1, 15 marks) | 例题2：评价价格上限（试卷一，15分）
Question: “Evaluate the decision of a government to impose a price ceiling on basic food items.”
题目：“评价政府对基本食品实行价格上限的决策。”
First, explain how a binding price ceiling set below the free-market equilibrium creates a persistent shortage. Show this with a diagram, marking Qd > Qs at the ceiling price.
首先，解释一个低于自由市场均衡的限价如何造成持续性短缺。用图表显示，在价格上限处 Qd > Qs。
The intended benefit is that low-income consumers can afford essential food, reducing poverty and improving equity. However, the shortage often leads to queuing, black markets where goods are sold at higher prices, and a reduction in quality as producers cut costs.
其预期好处是低收入消费者能买得起必需食品，从而减少贫困、促进公平。然而，短缺往往导致排长队、黑市（以更高价格出售商品）以及生产者因削减成本而降低质量。
Next, evaluate by considering different stakeholder groups: low-income households gain access albeit with waiting costs; producers may suffer lower revenues, potentially reducing future investment; the government may need to allocate resources to enforce the ceiling. The long-term effect could be a fall in supply if farmers switch to other crops.
接着，从不同利益相关者角度评价：低收入家庭虽获得购买机会但承担排队成本；生产者可能收入下降，减少未来投资；政府可能需要分配资源来执行限价。长期来看，如果农民改种其他作物，供给可能下降。
A judgment can be made that a price ceiling alone is not sufficient; targeted subsidies or income support may be more efficient. However, in emergency crises, a temporary ceiling can protect the vulnerable. The key is to balance short-term relief against market distortions.
可以做出判断：仅靠价格上限是不够的；有针对性的补贴或收入支持可能更有效。但在紧急危机中，临时限价可以保护弱势群体。关键在于权衡短期救济与市场扭曲。
4. Example 3: Data Response – Tariff Diagram (Paper 2) | 例题3：数据分析——关税图表（试卷二）
Scenario: The table shows the domestic supply and demand for Country X’s steel market before and after a tariff.
情景：下表显示了 X 国钢铁市场征收关税前后的国内供需数据。
| Price/tonne ($) | Domestic Qd (million tonnes) | Domestic Qs pre-tariff (million tonnes) | Domestic Qs post-tariff (million tonnes) |
| 400 | 20 | 8 | 12 |
| 500 | 16 | 10 | 14 |
| 600 | 12 | 12 | 16 |
Without trade, equilibrium is at $600. With free trade, world price is $400. The government imposes a $100 tariff per tonne.
无贸易时，均衡价格为600美元。自由贸易下，世界价格为400美元。政府每吨征收100美元关税。
Draw a diagram showing the world supply (horizontal at $400) and the new tariff-inclusive price at $500. Identify: domestic consumption falls from 20m to 16m tonnes; domestic production rises from 8m to 10m tonnes; imports shrink from 12m to 6m tonnes.
画出图表，显示世界供给（在400美元处水平）和新含税价格500美元。确定：国内消费从2000万吨降至1600万吨；国内生产从800万吨升至1000万吨；进口从1200万吨缩减至600万吨。
Calculate the tariff revenue: tax per unit × imports = $100 × 6m = $600 million. The welfare loss includes production inefficiency (higher-cost domestic production) and consumption inefficiency (lost consumer surplus). Reference the areas on the diagram and explain deadweight loss.
计算关税收入：单位税额×进口量 = 100美元×600万 = 6亿美元。福利损失包括生产低效（高成本的国内生产）和消费低效（消费者剩余损失）。在图中标明各区域并解释无谓损失。
In your answer, show the calculation steps and then evaluate whether the tariff benefits domestic steel producers at the expense of consumers and downstream industries. A data-based response earns high marks.
作答时，展示计算步骤，然后评价关税是否在牺牲消费者和下游产业的情况下惠及国内钢铁生产商。基于数据作答能获得高分。
5. Example 4: Calculating Price Elasticity of Demand (Paper 3) | 例题4：计算需求的价格弹性（试卷三）
Question: Price of a streaming service falls from $12 to $9 per month. Quantity demanded rises from 500,000 to 620,000 subscribers. Calculate PED using the midpoint method and interpret the result.
题目：某流媒体服务的价格从每月12美元降至9美元。需求量从50万用户升至62万用户。使用中点法计算需求的价格弹性，并解释结果。
Step 1: Compute the percentage change in quantity. Midpoint quantity = (500,000 + 620,000) / 2 = 560,000. Change in quantity = 120,000. %ΔQd = (120,000 / 560,000) × 100 ≈ 21.43%.
步骤1：计算需求量的百分比变化。中点数量 = (500,000 + 620,000) / 2 = 560,000。数量变化为120,000。%ΔQd = (120,000 / 560,000) × 100 ≈ 21.43%。
Step 2: Compute percentage change in price. Midpoint price = ($12 + $9) / 2 = $10.50. Change in price = $3. %ΔP = (3 / 10.50) × 100 ≈ 28.57%.
步骤2：计算价格的百分比变化。中点价格 = (12 + 9) / 2 = 10.50美元。价格变化为3美元。%ΔP = (3 / 10.50) × 100 ≈ 28.57%。
Then PED formula:
PED = %ΔQd ÷ %ΔP = 21.43% ÷ 28.57% ≈ 0.75
Since PED < 1, demand is inelastic. A 1% change in price leads to a 0.75% change in quantity demanded. Total revenue initially was $12 × 500,000 = $6 million. After price cut, revenue is $9 × 620,000 = $5.58 million, so revenue fell. This confirms inelastic demand as price and revenue move in the same direction.
由于 PED < 1，需求缺乏弹性。价格变化1%导致需求量变化0.75%。初始总收入为12美元×50万 = 600万美元。降价后，收入为9美元×62万 = 558万美元，收入下降。这验证了需求缺乏弹性时价格与收入同向变动。
In exams, always show full workings and link the PED coefficient to the firm’s pricing strategy.
考试中，始终展示完整计算过程，并将弹性系数与企业的定价策略相联系。
6. Example 5: Opportunity Cost & Production Possibility Curve | 例题5：机会成本与生产可能性曲线
Question: An economy produces capital goods and consumer goods. Moving from point A (80 capital, 40 consumer) to point B (60 capital, 70 consumer), calculate the opportunity cost of producing one more consumer good.
题目：某经济体生产资本品和消费品。从点A（80资本品, 40消费品）移动到点B（60资本品, 70消费品），计算多生产一单位消费品的机会成本。
Identify the changes: capital goods decrease by 20 units, consumer goods increase by 30 units. The opportunity cost of the 30 additional consumer goods is 20 capital goods sacrificed.
确定变化：资本品减少20单位，消费品增加30单位。新增30单位消费品的机会成本是放弃的20单位资本品。
Thus, per consumer good opportunity cost = 20/30 = 2/3 (approx 0.67) capital goods per consumer good. This reflects increasing opportunity cost if the PPC is bowed outward.
因此，每单位消费品的机会成本 = 20/30 = 2/3（约0.67）单位资本品。这反映了如果PPC是向外凸出的形状，则机会成本递增。
Diagram explanation: On a concave PPC, the slope steepens as we produce more consumer goods, representing the law of increasing opportunity cost. Mention that resources are not equally suited to produce both goods.
图表解释：在凹形PPC上，随着消费品产量增加，斜率变陡，这代表机会成本递增规律。应提及资源并非同等适用于生产两种商品。
This simple calculation often appears in Paper 3. Make sure you label axes, points and show the trade-off clearly on the diagram.
这种简单计算经常出现在试卷三中。确保在图表上标注坐标轴、点，并清楚显示权衡关系。
7. Example 6: Negative Externality and Deadweight Loss | 例题6：负外部性与无谓损失
Question: “Explain why the production of a good with negative externalities results in a deadweight loss, using a diagram.”
题目：“用图表解释为何具有负外部性的商品生产会导致无谓损失。”
Draw the market with Marginal Private Cost (MPC) and Marginal Social Cost (MSC), where MSC lies above MPC due to external costs like pollution. Demand reflects Marginal Private Benefit (MPB), assumed equal to Marginal Social Benefit (MSB).
画出边际私人成本（MPC）和边际社会成本（MSC）曲线，由于污染等外部成本，MSC位于MPC之上。需求反映边际私人收益（MPB），假定等于边际社会收益（MSB）。
The free-market equilibrium is where MPB = MPC at quantity Qm, and price Pm. The socially optimal quantity is where MSB = MSC at Qopt. Since Qm > Qopt, too much of the good is produced.
自由市场均衡在 MPB = MPC 处，对应数量 Qm 和价格 Pm。社会最优数量在 MSB = MSC 处，对应 Qopt。由于 Qm > Qopt，商品被过度生产。
The deadweight loss is the triangle area between MSC and MSB from Qopt to Qm, representing the excess social cost over benefit for those units. Label this area clearly on your diagram and shade it.
无谓损失是位于 Qopt 到 Qm 之间 MSC 与 MSB 之间的三角区域，代表那些单位的社会成本超过收益的部分。在图上清晰标出并涂上阴影。
Define that deadweight loss is the loss of social welfare due to market failure. In evaluation, mention corrective policies such as a Pigouvian tax equal to the external cost at Qopt, which shifts MPC up to MSC, internalising the externality.
定义无谓损失为市场失灵造成的社会福利损失。在评价中，提及矫正性政策，如等于最优产量下外部成本的庇古税，把MPC上移至MSC，从而将外部性内部化。
8. Example 7: Macroeconomic Policy Trade-offs | 例题7：宏观经济政策权衡
Question: “Discuss the trade-offs a government might face when using expansionary fiscal policy to reduce unemployment.”
题目：“讨论政府在使用扩张性财政政策降低失业时可能面临的政策权衡。”
Start with AD-AS diagram: Increase in government spending or tax cuts shift aggregate demand (AD) to the right, causing real GDP to rise and unemployment to fall. However, the price level increases, leading to demand-pull inflation.
从 AD-AS 图开始：增加政府支出或减税使总需求（AD）右移，导致实际GDP上升、失业下降。但价格水平上升，引发需求拉动型通胀。
There is a short-run Phillips curve trade-off between inflation and unemployment. As unemployment falls, inflation rises. If the economy is near full employment (vertical LRAS), the inflationary impact is stronger with little real output gain.
在短期菲利普斯曲线中，通胀与失业之间存在权衡。随着失业下降，通胀上升。如果经济接近充分就业（LRAS垂直），通胀影响更强，而实际产出增长微弱。
Other trade-offs: Budget deficit may increase, raising national debt and potentially crowding out private investment. Currency may depreciate if inflation erodes competitiveness, affecting trade balance.
其他权衡：预算赤字可能增加，推高国债，并可能挤出私人投资。如果通胀侵蚀竞争力，货币可能贬值，影响贸易平衡。
Evaluate: The trade-offs depend on the stage of the economic cycle. In a deep recession with spare capacity, expansionary policy can be effective without significant inflation. A judgment might suggest combining fiscal policy with supply-side policies to shift LRAS right, alleviating the trade-off.
评价：这些权衡取决于经济周期的阶段。在深度衰退且存在闲置产能时，扩张性政策可能有效且不会引发严重通胀。一个判断可能是将财政政策与供给侧政策结合，右移LRAS，从而缓和权衡。
Always support your discussion with real-world examples, such as the US fiscal stimulus in 2009.
始终用现实案例支撑论述，如2009年美国财政刺激计划。
9. Example 8: Real GDP vs Nominal GDP Calculation | 例题8：实际GDP与名义GDP的计算
Question: In 2023, Country A’s nominal GDP was $800 billion. The GDP deflator (price index) was 125. Calculate real GDP for 2023 and explain what it means. (Base year index = 100)
题目：2023年A国名义GDP为8000亿美元，GDP平减指数为125。计算2023年实际GDP并解释其含义。（基年指数 = 100）
The relationship is:
Real GDP = (Nominal GDP / Price Deflator) × 100
Substitute values:
Real GDP = (800 billion / 125) × 100 = 6.4 × 100 = $640 billion
Real GDP removes the effect of price changes, showing that the actual volume of goods and services produced is worth $640 billion at base-year prices. This allows meaningful comparison over time.
实际GDP剔除了价格变动的影响，表明以基年价格计算的商品与服务实际产量价值为6400亿美元。这使跨期比较变得有意义。
Explain that if nominal GDP grew by 8% but the deflator shows 5% inflation, real growth was only about 2.86%. Use this to link to economic well-being and standard of living.
解释如果名义GDP增长8%，但平减指数显示5%的通胀，实际增长仅约2.86%。据此联系经济福祉和生活水平。
In Paper 3, such calculations must be precise. Also be ready to convert nominal GDP to GDP per capita and discuss limitations.
在试卷三中，此类计算必须精确。同时要准备好将名义GDP转化为人均GDP并讨论其局限性。
10. Key Tips for Evaluation Questions | 评价题的答题技巧
To consistently score high on 15-mark evaluation questions, structure your conclusion around ‘CLASPP’: Conclusion, Long-term vs short-term, Assumptions, Stakeholders, Priorities, Pros and cons.
为在15分评价题中持续获得高分，围绕“CLASPP”组织你的结论：结论本身、长期与短期、假设条件、利益相关者、优先次序、赞成与反对理由。
Never just summarise; weigh arguments and state under what conditions a policy works best. For instance, a tax on sugary drinks may be effective if demand is elastic and alternatives exist.
绝不要只做总结；要权衡论点，并说明在何种条件下政策最有效。例如，对含糖饮料征税在需求富有弹性且存在替代品时可能有效。
Use diagrams to show welfare effects, and refer to real-world context to demonstrate depth. Avoid listing advantages and disadvantages separately without linking them to the judgment.
使用图表展示福利效果，并引用现实背景来展示深度。避免脱节地罗列优缺点，而不将其与判断联系起来。
Time management: Spend roughly 5 minutes planning. Jot down the key stakeholder effects, a relevant example, and your final verdict. This makes your answer coherent and sophisticated.
时间管理：大约花5分钟规划。草草记下关键的利益相关者影响、一个相关例子以及你的最终定论。这使你的答案前后连贯、有深度。
Practice applying these tips to past-paper questions under timed conditions. Review mark schemes to see how examiners allocate marks for evaluation.
在计时条件下练习将这些技巧运用于历年试题。查阅评分方案，了解考官如何为评价部分分配分数。
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