IGCSE CIE Economics: Common Mistakes and Tricky Questions Explained | IGCSE CIE 经济：易错题精讲

📚 IGCSE CIE Economics: Common Mistakes and Tricky Questions Explained | IGCSE CIE 经济：易错题精讲

IGCSE CIE Economics papers often contain questions that test subtle distinctions. Many candidates lose marks by confusing fundamental concepts, misinterpreting diagrams, or applying the wrong logic to calculations. This article dissects the most frequent pitfalls, clarifies the correct reasoning, and provides model exam-style questions to help you avoid common errors. Read through each section carefully, and you will sharpen your exam technique significantly.

IGCSE CIE 经济试卷常常考查细微的区分。许多考生因混淆基本概念、误读图示或在计算时用错逻辑而丢分。本文剖析最常见的陷阱，厘清正确思路，并提供模拟考试题帮助你避开易错点。仔细阅读每节内容，你的应试技巧会显著提升。

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1. Demand: Change in Quantity Demanded vs. Change in Demand | 需求量变动与需求变动

A classic blunder is to say that a fall in the price of a good “increases demand”. The correct statement is that a fall in price causes an extension of quantity demanded – a movement down along the existing demand curve. Demand itself (the entire curve) only shifts when a non-price determinant changes, such as income, tastes, the price of substitutes or complements, population, or advertising.

一个典型的错误是说商品价格下降“增加了需求”。正确的表述是价格下降引起需求量增加——沿着原有需求曲线向下移动。需求本身（整条曲线）位移，只有当非价格决定因素变化时才会发生，例如收入、偏好、替代品或互补品的价格、人口或广告。

Common exam trap: “The government imposes a tax on sugary drinks. What is the impact?” Many students answer “quantity demanded decreases”. The tax raises the price for consumers, so there is a movement along the demand curve (a contraction in quantity demanded). However, the tax is often a supply-side shock; the demand curve does not shift unless tastes change as a result. Be precise: a change in the good’s own price always causes a movement along the curve, never a shift.

常见考试陷阱：“政府对含糖饮料征税，会有什么影响？”许多学生回答“需求量减少”。税收提高了消费者支付的价格，因此是沿着需求曲线移动（需求量收缩）。然而，税收通常是供给侧冲击；除非因此改变了偏好，否则需求曲线不会位移。要精准：商品自身价格的变化总是引起沿曲线移动，绝不会使曲线位移。

Example question: A cinema reduces its ticket prices by 20%. Which of the following is correct? A) Demand for cinema visits increases. B) Demand for cinema visits shifts to the right. C) Quantity demanded of cinema visits increases. D) The demand curve for cinema visits becomes steeper.
Answer: C. The price change affects the quantity demanded, not demand.

例题：一家电影院将票价降低20%。以下哪项正确？A) 看电影的需求增加。B) 看电影的需求曲线向右移动。C) 看电影的需求量增加。D) 看电影的需求曲线变得更陡。
答案：C。价格变动影响的是需求量，不是需求。

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2. Supply: Movement Along vs. Shift of the Supply Curve | 供给量变动与供给曲线位移

Just like demand, supply has its own common confusion. A rise in the price of a good leads to an expansion of quantity supplied (a movement up along the supply curve). The supply curve shifts only when conditions of production change: costs of raw materials, technology, indirect taxes, subsidies, number of sellers, or weather for agricultural goods.

与需求一样，供给也有常见的混淆点。商品价格上升导致供给量增加（沿着供给曲线向上移动）。供给曲线只有在生产条件改变时才会位移：原材料成本、技术、间接税、补贴、卖者数量或影响农业的气候。

Typical mistake: “An increase in the price of coffee increases supply.” In fact, the higher price makes it more profitable to supply more, so quantity supplied expands along the existing curve. If a new irrigation system reduces production costs, that would shift the supply curve to the right – an increase in supply.

典型错误：“咖啡价格上升增加了供给。”实际上，更高的价格使供给更有利可图，因此供给量沿现有曲线增加。如果新的灌溉系统降低了生产成本，那会使供给曲线向右移动——这才是供给增加。

Exam-style question: A technological advance allows car producers to halve assembly time. What is the effect on the car market? A) Quantity supplied of cars increases. B) Supply of cars increases. C) Both demand and supply increase. D) The supply curve becomes flatter.
Answer: B. Better technology is a non-price determinant that shifts the supply curve to the right.

模拟题：技术进步使汽车装配时间减半。对汽车市场有何影响？A) 汽车供给量增加。B) 汽车供给增加。C) 需求和供给都增加。D) 供给曲线变得更平坦。
答案：B。技术改善是非价格决定因素，使供给曲线向右移动。

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3. Calculating Opportunity Cost Correctly | 正确计算机会成本

Opportunity cost is the next best alternative forgone. When using a production possibility curve (PPC) table, many students simply state the amount of goods sacrificed rather than the ratio per unit. The opportunity cost of producing one extra unit of good X is the amount of good Y given up divided by the gain in X.

机会成本是所放弃的次优选择。在使用生产可能性曲线（PPC）的数据表时，许多学生只说出牺牲的商品数量，而没有说出每单位的比率。多生产一单位商品X的机会成本，是放弃的商品Y的数量除以X的增加量。

Common error illustrated: An economy can produce either 100 food or 50 clothing. Moving from 0 to 30 clothing, it sacrifices 20 food. The opportunity cost of producing one unit of clothing is 20/30 = 0.67 food. A careless answer would be “20 food”. Always express opportunity cost as a ratio per unit of the good gained.

易错示例：一个经济体可以生产100单位粮食或50单位服装。从0服装增产到30服装，它牺牲了20单位粮食。生产一单位服装的机会成本是20/30 = 0.67单位粮食。粗心的答案会写成“20单位粮食”。始终要把机会成本表示为每获得一单位商品所放弃的数量。

Exam tip: When a PPC is drawn as a straight line, opportunity cost is constant. When it is concave (bowed out), opportunity cost increases as more of one good is produced. Questions frequently test this conceptual link.

考试提示：当PPC是一条直线时，机会成本不变。当PPC凹向原点时，随着一种商品生产增加，机会成本递增。考题经常测试这一概念联系。

Question: A farmer can produce 200 kg of wheat or 100 kg of rice on a fixed plot. The PPC is linear. What is the opportunity cost of producing 1 kg of rice? A) 2 kg of wheat. B) 0.5 kg of wheat. C) 100 kg of wheat. D) 200 kg of wheat.
Answer: A. For every 1 kg of rice produced, 2 kg of wheat are sacrificed (200/100).

问题：一个农民在固定土地上可以生产200公斤小麦或100公斤稻米。PPC是线性的。生产1公斤稻米的机会成本是多少？A) 2公斤小麦。B) 0.5公斤小麦。C) 100公斤小麦。D) 200公斤小麦。
答案：A。每生产1公斤稻米，要放弃2公斤小麦（200/100）。

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4. Points On, Inside and Outside the PPC | 生产可能性曲线上的点、内部点和外部点

A point on the PPC represents productive efficiency – all resources are fully and efficiently employed. A point inside the PPC indicates unemployment or inefficient use of resources. A point outside the PPC is unattainable given current resources and technology. However, a common misconception is that an outside point is always impossible. In the long run, economic growth (an increase in the quantity or quality of resources) can shift the PPC outward, making previously unattainable points achievable. International trade also allows a country to consume beyond its PPC.

在PPC上的点代表生产效率——所有资源被充分且有效地利用。PPC内部的点表示失业或资源使用无效率。在当前资源和技术下，PPC外部的点是无法实现的。但常见的误解是外部点永远不可能达到。长期中，经济增长（资源数量或质量的提升）可以使PPC向外移动，从而使原先无法达到的点成为可能。国际贸易也可以让一个国家消费超越其PPC。

Exam trick: “Which point could occur after investment in capital goods?” Investment increases future productive capacity, so the whole PPC shifts outward. A point that was previously outside can now lie on the new PPC.

考试技巧：“投资资本品后，哪个点可能出现？”投资提高了未来的生产能力，因此整条PPC向外移动。先前在外部的一个点，现在可能落在新的PPC上。

Quick check: Inside point → unemployment/recession. Point on curve → efficient. Outside point → unattainable without growth or trade. Always read the question to see whether it asks about the short run or long run.

快速检测：内部点 → 失业/衰退。曲线上的点 → 有效率。外部点 → 无经济增长或贸易则无法实现。一定要看清题目问的是短期还是长期。

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5. Price Elasticity of Demand (PED) and Total Revenue | 需求价格弹性与总收入

The relationship between PED and total revenue is a frequent source of error. If demand is price inelastic (PED < 1), a price rise increases total revenue because the percentage fall in quantity demanded is smaller than the percentage rise in price. If demand is price elastic (PED > 1), a price rise reduces total revenue because the quantity drop outweighs the price increase. Many students reverse this logic or forget to consider revenue direction.

需求价格弹性（PED）与总收入的关系经常出错。如果需求缺乏弹性（PED < 1），提价会增加总收入，因为需求量下降百分比小于价格上涨百分比。如果需求富有弹性（PED > 1），提价会减少总收入，因为数量减少的幅度超过了价格上升的幅度。很多学生会把这一逻辑记反，或忘记考虑收入的变化方向。

PED = %ΔQd / %ΔP

Use a simple truth table to memorise the linkage:

PED	Price change	Total Revenue
Inelastic (< 1)	Increase	Increases
Inelastic (< 1)	Decrease	Decreases
Elastic (> 1)	Increase	Decreases
Elastic (> 1)	Decrease	Increases

Memory aid: For inelastic demand, price and total revenue move in the same direction. For elastic demand, they move in opposite directions.

记忆技巧：缺乏弹性时，价格与总收入同方向变动。富有弹性时，两者反方向变动。

Example question: A firm sells 500 units at £10 each. PED is 0.8. If it raises the price to £12, what should happen to total revenue? A) Fall to £5 000. B) Rise above £5 000. C) Remain at £5 000. D) Fall because demand is elastic.
Answer: B. Since PED is 0.8 (inelastic), the price hike increases total revenue despite a fall in sales volume.

例题：一家公司以每件£10售出500件。PED为0.8。若提价至£12，总收入会如何？A) 降至£5 000。B) 升至£5 000以上。C) 保持£5 000。D) 下降，因为需求有弹性。
答案：B。因为PED=0.8（缺乏弹性），提价虽使销量减少，但总收入增加。

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6. Incidence of an Indirect Tax | 间接税的归宿

When a government imposes an indirect tax (e.g. a specific tax per unit), the supply curve shifts vertically upward by the amount of the tax. Students often assume the entire tax is passed on to consumers. In reality, the burden is shared between consumers and producers. The division depends on the relative price elasticities of demand and supply.

当政府征收间接税（如每单位从量税），供给曲线垂直上移税额的幅度。学生们经常假设税收全部由消费者承担。实际上，税负在消费者和生产者之间分摊。分摊比例取决于需求与供给的相对价格弹性。

Key rule: The more inelastic the demand, the greater the burden on consumers. The more inelastic the supply, the greater the burden on producers. If demand is perfectly inelastic (vertical curve), the consumers’ price rises by the full amount of the tax. If demand is perfectly elastic, the producers bear the entire tax.

关键规则：需求越缺乏弹性，消费者承担的税负越重。供给越缺乏弹性，生产者承担的税负越重。如果需求完全无弹性（垂直的曲线），消费者支付价格全额上升税额。如果需求完全弹性，生产者承担全部税收。

Common exam pitfall: Drawing tax diagrams incorrectly or labelling the new price as the full tax passed on. Always show the vertical gap between the original and new supply curve; the vertical difference between the original and new equilibrium price is the consumers’ share, and the rest is the producers’ share.

常见考试陷井：绘制税收图示时错误，或将新价格标注为全额转嫁。必须画出原供给曲线与新供给曲线的垂直差距；原均衡价格与新均衡价格之间的垂直差是消费者负担部分，剩余的是生产者负担部分。

Question: The demand for insulin is perfectly inelastic

Published by TutorHao | IGCSE Economics Revision Series | aleveler.com

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