KS3 CAIE Economics: Quick Reference Handbook of Formulas and Principles | KS3 CAIE 经济：公式定理速查手册

📚 KS3 CAIE Economics: Quick Reference Handbook of Formulas and Principles | KS3 CAIE 经济：公式定理速查手册

Welcome to your go-to quick reference handbook for KS3 CAIE Economics. This guide brings together the essential formulas, principles, and key concepts you will encounter in your studies. Whether you are revising for an exam or just need a clear summary, each section provides concise explanations in both English and Chinese, followed by the relevant formulas set out in a clear, easy-to-read format. Master the fundamentals of scarcity, demand and supply, elasticity, costs, market equilibrium and more, all in one place.

欢迎使用这本 KS3 CAIE 经济公式定理速查手册。本手册汇集了你在学习过程中会遇到的基本公式、定理和核心概念。无论你是为考试复习，还是只需要一份清晰的总结，每个部分都提供了中英文双语简明解释，并附有清晰易读的公式格式。一册在手，便可掌握稀缺性、需求与供给、弹性、成本、市场均衡等基础知识。

1. Scarcity and Opportunity Cost | 稀缺性与机会成本

Scarcity is the fundamental economic problem of having limited resources but unlimited wants. Because resources are finite, choices must be made about how to allocate them. Every choice involves a trade-off.

稀缺性是指资源有限而欲望无限这一基本经济问题。由于资源是有限的，我们必须对如何使用资源做出选择。每一个选择都伴随着权衡取舍。

Opportunity cost is the value of the next best alternative that is forgone when a choice is made. It is not simply the money spent, but the benefit lost from the option not chosen.

机会成本是指做出某种选择时所放弃的次优选项的价值。它不仅仅是花掉的钱，而是没有选择的那一选项所失去的收益。

Understanding scarcity and opportunity cost helps individuals, businesses and governments make rational decisions about resource use.

理解稀缺性和机会成本有助于个人、企业和政府就资源使用做出理性决策。

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2. Factors of Production | 生产要素

The resources used to produce goods and services are called factors of production. They are traditionally grouped into four categories: land, labour, capital and enterprise.

用于生产商品和服务的资源被称为生产要素。传统上它们分为四类：土地、劳动、资本和企业家才能。

Land includes all natural resources such as water, minerals, forests and fertile soil. Labour refers to the human effort, both physical and mental, used in production. Capital consists of man-made tools, machinery, buildings and equipment used to produce other goods. Enterprise is the ability to combine the other factors, take risks and innovate.

土地包括所有自然资源，如水源、矿产、森林和肥沃的土壤。劳动指生产中投入的人类体力和脑力努力。资本包括人造工具、机器、建筑物和用于生产其他物品的设备。企业家才能则是指组合其他生产要素、承担风险并进行创新的能力。

These factors earn rewards: land earns rent, labour earns wages, capital earns interest and enterprise earns profit.

这些生产要素获得相应的报酬：土地获得地租，劳动获得工资，资本获得利息，企业家才能获得利润。

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3. Demand and the Law of Demand | 需求与需求定律

Demand is the quantity of a good or service that consumers are willing and able to purchase at various prices over a given period of time. It is not just a desire; effective demand requires both willingness and ability to pay.

需求是指消费者在给定时间段内，在不同价格水平下愿意且能够购买的商品或服务的数量。这不只是一种欲望；有效需求需要支付意愿和支付能力两者兼备。

The law of demand states that, ceteris paribus (all other things being equal), as the price of a good increases, the quantity demanded decreases, and as the price falls, the quantity demanded rises. This inverse relationship creates a downward-sloping demand curve.

需求定律指出，在其他条件相同的情况下，当商品价格上升时，需求量下降；当价格下降时，需求量上升。这种反向关系形成一条向下倾斜的需求曲线。

A change in the price of the good itself causes a movement along the demand curve, while changes in other factors such as income, tastes or the prices of related goods cause the entire demand curve to shift.

商品本身价格的变化导致需求量沿需求曲线移动，而收入、偏好或相关商品价格等其他因素的变化则导致整条需求曲线位移。

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4. Supply and the Law of Supply | 供给与供给定律

Supply is the quantity of a good or service that producers are willing and able to offer for sale at different prices over a given period. Producers aim to maximise profits, so higher prices generally encourage a greater quantity supplied.

供给是指生产者在给定时间段内，在不同价格水平下愿意且能够提供出售的商品或服务的数量。生产者的目标是利润最大化，因此更高的价格通常会鼓励更多的供给量。

The law of supply states that, ceteris paribus, as the price of a good rises, the quantity supplied increases, and as the price falls, the quantity supplied decreases. This direct relationship gives the supply curve its upward slope.

供给定律指出，在其他条件不变的情况下，当商品价格上升时，供给量增加；当价格下降时，供给量减少。这种正向关系使供给曲线向上倾斜。

Movements along the supply curve are caused by changes in price, while shifts of the curve result from changes in factors such as production costs, technology, taxes, subsidies and the number of sellers.

价格变动导致供给量沿供给曲线移动，而生产成本、技术、税收、补贴和卖方数量等因素的变化则导致整条供给曲线位移。

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5. Price Elasticity of Demand | 需求的价格弹性

Price elasticity of demand (PED) measures how responsive the quantity demanded of a good is to a change in its price. It helps firms predict the impact of pricing decisions on total revenue.

需求的价格弹性（PED）衡量的是某种商品的需求量对该商品价格变化的反应程度。它帮助企业预测价格决策对总收入的影响。

The formula for PED is:

PED = %ΔQd ÷ %ΔP

需求价格弹性的计算公式为需求量变动的百分比除以价格变动的百分比。

The value of PED indicates the type of elasticity:

• If PED > 1, demand is price elastic (quantity changes more than price).
• If PED < 1, demand is price inelastic (quantity changes less than price).
• If PED = 1, demand is unit elastic.
• If PED = 0, demand is perfectly inelastic.
• If PED = ∞, demand is perfectly elastic.

PED 的数值表示弹性类型：

• PED > 1，需求富有价格弹性（数量变化大于价格变化）；
• PED < 1，需求缺乏价格弹性（数量变化小于价格变化）；
• PED = 1，需求具有单位弹性；
• PED = 0，需求完全无弹性；
• PED = ∞，需求完全有弹性。

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6. Costs of Production | 生产成本

Understanding costs is essential for businesses to set prices and aim for profitability. Total cost (TC) is divided into fixed costs (FC) and variable costs (VC).

理解成本对于企业定价和追求盈利至关重要。总成本（TC）分为固定成本（FC）和可变成本（VC）。

Key cost formulas:

TC = FC + VC

关键成本计算公式：总成本等于固定成本加可变成本。

AC = TC ÷ Q

平均成本（AC）等于总成本除以产量 Q。

AFC = FC ÷ Q

平均固定成本（AFC）等于固定成本除以产量。

AVC = VC ÷ Q

平均可变成本（AVC）等于可变成本除以产量。

Fixed costs do not vary with output in the short run (e.g. rent, insurance), while variable costs change directly with the level of production (e.g. raw materials, direct labour).

在短期内，固定成本不随产量变化（如租金、保险），而可变成本直接随生产水平变化（如原材料、直接人工）。

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7. Revenue and Profit | 收入与利润

Revenue is the income received by a firm from selling its products. Total revenue (TR) is calculated by multiplying the price per unit by the quantity sold.

收入是企业通过销售产品获得的进账。总收入（TR）由单位价格乘以销售数量计算得出。

TR = P × Q

总收入等于价格乘以数量。

Profit is the difference between total revenue and total cost. It is the reward for enterprise.

利润是总收入与总成本之间的差额，它是企业家才能的报酬。

Profit = TR − TC

利润等于总收入减去总成本。

A firm can also calculate its break-even point, the level of output where total revenue equals total cost and profit is zero. The break-even formula (using contribution per unit) is:

企业还可以计算盈亏平衡点，即总收入等于总成本、利润为零的产量水平。盈亏平衡公式（使用单位贡献）为：

Break-even output = FC ÷ (P − AVC)

盈亏平衡产量等于固定成本除以（价格减去平均可变成本）。

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8. Market Equilibrium | 市场均衡

Market equilibrium occurs at the price where the quantity demanded by consumers equals the quantity supplied by producers. At this point, there is no tendency for the price to change.

市场均衡出现在消费者需求量等于生产者供给量的价格水平上。在这一点，价格没有变动的趋势。

The equilibrium price (also called the market-clearing price) and equilibrium quantity are determined by the intersection of the demand and supply curves.

均衡价格（又称市场出清价格）和均衡数量由需求曲线与供给曲线的交点决定。

If the market price is set above equilibrium, a surplus (excess supply) occurs, putting downward pressure on price. If the price is below equilibrium, a shortage (excess demand) emerges, pushing the price upward. This process continues until equilibrium is restored.

若市场价格高于均衡水平，就会出现过剩（超额供给），对价格形成下行压力；若价格低于均衡水平，则出现短缺（超额需求），推动价格上升。这一过程将持续直至重新达到均衡。

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9. Money and Inflation | 货币与通货膨胀

Money serves as a medium of exchange, a unit of account, a store of value and a standard of deferred payment. Inflation is a sustained increase in the general price level of goods and services in an economy over time.

货币充当交换媒介、计价单位、价值贮藏和延期支付的标准。通货膨胀是指一个经济体中商品和服务的总体价格水平在一段时间内持续上涨。

The inflation rate can be calculated using a price index such as the Consumer Price Index (CPI):

Inflation rate = [(CPI current year − CPI previous year) ÷ CPI previous year] × 100%

通货膨胀率可通过消费者价格指数（CPI）等价格指数计算，公式为：（当年CPI减去上年CPI）除以上年CPI，再乘以100%。

A simplified form of the quantity theory of money shows the relationship between money supply and prices: MV = PT, where M is money supply, V is velocity of circulation, P is price level and T is the number of transactions. An increase in M, if V and T are stable, leads to a rise in P.

货币数量论的一个简化形式显示了货币供给与价格之间的关系：MV = PT，其中M是货币供给，V是货币流通速度，P是价格水平，T是交易数量。如果V和T保持稳定，M的增加会导致P上升。

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10. International Trade and Exchange Rates | 国际贸易与汇率

International trade allows countries to specialise in producing goods where they have a comparative advantage, leading to greater global efficiency and consumption. Exports are goods sold abroad, while imports are goods bought from abroad.

国际贸易使各国能够专门生产其具有比较优势的商品，从而提高全球效率和消费水平。出口是在国外销售的商品，进口是从国外购买的商品。

The balance of trade is the difference between the value of a country’s exports and imports. A trade surplus occurs when exports exceed imports, while a trade deficit occurs when imports exceed exports.

贸易差额是一国出口总值与进口总值之差。当出口大于进口时，出现贸易顺差；当进口大于出口时，出现贸易逆差。

The exchange rate is the price of one currency in terms of another. If the exchange rate of a country’s currency appreciates, its exports become more expensive for foreign buyers and imports become cheaper. If it depreciates, exports become cheaper and imports more expensive.

汇率是一种货币用另一种货币表示的价格。如果一国货币升值，其出口对外国买家来说更昂贵，进口变得更便宜；如果货币贬值，出口变得更便宜，进口则更昂贵。

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Published by TutorHao | Economics Revision Series | aleveler.com

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