📚 Year 10 WJEC Economics: Formula & Theorem Quick Reference Handbook | Year 10 WJEC 经济：公式定理速查手册
This quick-reference handbook brings together all the essential formulas, theorems and key relationships that you need to master for Year 10 WJEC Economics. It covers microeconomic principles such as demand, supply and elasticity, as well as macroeconomic indicators including GDP, inflation and unemployment. Use it regularly to check your understanding and build confidence for assessments.
这本速查手册汇集了你需要掌握的 Year 10 WJEC 经济所有关键公式、定理和重要关系。它涵盖了需求、供给和弹性等微观经济原理，以及 GDP、通货膨胀和失业等宏观经济指标。定期使用它来检验你的理解，并为考试建立信心。
1. Fundamental Principles & Opportunity Cost | 基本原则与机会成本
The basic economic problem is scarcity: finite resources cannot satisfy all human wants. This forces individuals, firms and governments to make choices, and every choice involves a trade-off.
基本经济问题是稀缺性：有限的资源无法满足无限的人类需求。这迫使个人、企业和政府做出选择，而每一个选择都涉及权衡取舍。
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 taken.
机会成本是做出一项选择时所放弃的次优替代品的价值。它不仅指花费的金钱，还包括未被选中方案所失去的收益。
Opportunity Cost = Value of Next Best Alternative Given Up
机会成本 = 所放弃的次优替代品的价值
The production possibility frontier (PPF) illustrates opportunity cost, showing the maximum combinations of two goods an economy can produce with given resources.
生产可能性边界 (PPF) 可以说明机会成本，它展示了一个经济体在给定资源下能够生产的两种商品的最大组合。
2. Law of Demand & Law of Supply | 需求定理与供给定理
The law of demand states that, ceteris paribus, as the price of a good rises, the quantity demanded falls. This inverse relationship is shown by a downward-sloping demand curve.
需求定理指出，在其他条件不变的情况下，商品价格上升，需求量下降。这种反比关系表现为一条向下倾斜的需求曲线。
The law of supply states that, ceteris paribus, as the price of a good rises, the quantity supplied rises. Producers are willing to supply more at higher prices because of the profit motive, creating an upward‑sloping supply curve.
供给定理指出，在其他条件不变的情况下，商品价格上升，供给量上升。受利润动机驱使，生产者在更高价格下愿意供给更多，从而形成向上倾斜的供给曲线。
A change in price leads to a movement along the demand or supply curve. A change in any other factor (e.g. income, costs of production) shifts the entire curve.
价格的变化导致沿需求曲线或供给曲线的移动。任何其他因素的变化（如收入、生产成本）则会使整条曲线发生位移。
3. Price Elasticity of Demand (PED) | 需求价格弹性 (PED)
Price elasticity of demand measures the responsiveness of quantity demanded to a change in the good’s own price. It is calculated using the formula:
需求价格弹性衡量需求量对商品自身价格变化的反应程度。其计算公式为：
PED = %Δ Quantity Demanded ÷ %Δ Price
PED = 需求量变化百分比 ÷ 价格变化百分比
A PED value greater than 1 indicates elastic demand – consumers are very responsive to price changes. Goods with many substitutes or luxury items typically have elastic demand.
PED 值大于 1 表示需求富有弹性——消费者对价格变化非常敏感。拥有众多替代品的商品或奢侈品通常需求富有弹性。
A PED value less than 1 indicates inelastic demand – quantity demanded changes by a smaller percentage than price. Necessities and goods with few substitutes tend to be inelastic.
PED 值小于 1 表示需求缺乏弹性——需求量变化的百分比小于价格变化的百分比。生活必需品和替代品较少的商品往往缺乏弹性。
If PED equals exactly 1, demand is unit elastic, meaning the percentage change in quantity demanded equals the percentage change in price.
如果 PED 恰好等于 1，则需求为单位弹性，意味着需求量变化的百分比等于价格变化的百分比。
PED is also crucial for revenue analysis. When demand is elastic, a price fall raises total revenue; when inelastic, a price fall reduces total revenue.
PED 对收入分析也十分关键。当需求富有弹性时，降价会提高总收入；当需求缺乏弹性时，降价则会降低总收入。
4. Income Elasticity & Price Elasticity of Supply (YED & PES) | 收入弹性与供给价格弹性 (YED & PES)
Income elasticity of demand (YED) measures how quantity demanded responds to a change in consumers’ income.
需求收入弹性 (YED) 衡量需求量对消费者收入变化的反应程度。
YED = %Δ Quantity Demanded ÷ %Δ Income
YED = 需求量变化百分比 ÷ 收入变化百分比
A positive YED means the good is normal – as income rises, demand increases. A negative YED indicates an inferior good, where demand falls when income rises.
正的 YED 意味着商品是正常品——收入增加，需求增加。负的 YED 表明商品是低档品，收入增加时需求下降。
Price elasticity of supply (PES) measures how quantity supplied responds to a change in price.
供给价格弹性 (PES) 衡量供给量对价格变化的反应程度。
PES = %Δ Quantity Supplied ÷ %Δ Price
PES = 供给量变化百分比 ÷ 价格变化百分比
PES values tend to be higher when firms can quickly adjust production and have spare capacity. Agricultural goods often have a low PES in the short run because supply cannot respond instantly.
当企业能够迅速调整生产且存在闲置产能时，PES 值往往较高。农产品在短期内通常 PES 较低，因为供给无法即刻做出反应。
5. Market Equilibrium & Price Mechanism | 市场均衡与价格机制
Market equilibrium occurs where the quantity demanded equals the quantity supplied. At the equilibrium price, there is no excess demand or excess supply.
市场均衡发生在需求量等于供给量时。在均衡价格下，不存在超额需求或超额供给。
Equilibrium: Qd = Qs
均衡: Qd = Qs
When price is above equilibrium, a surplus (excess supply) arises, putting downward pressure on price. When price is below equilibrium, a shortage (excess demand) drives the price up.
当价格高于均衡价格时，出现过剩（超额供给），价格面临下行压力。当价格低于均衡价格时，出现短缺（超额需求），推动价格上升。
The price mechanism performs three key functions: signalling – prices indicate where resources are needed; incentive – higher prices encourage producers to supply more; and rationing – scarce goods go to those willing and able to pay.
价格机制发挥三大功能：信号功能——价格指示资源需要流向何处；激励功能——高价鼓励生产者增加供给；配给功能——稀缺商品分配给愿意且有能力支付的人。
6. Costs of Production, Revenue & Profit | 生产成本、收益与利润
Understanding costs and revenues is vital for analysing firm behaviour. The table below summarises the key formulas.
理解成本与收益对分析企业行为至关重要。下表总结了关键公式。
| Term (术语) | Formula (公式) |
|---|---|
| Total Fixed Cost (TFC) | Constant, does not vary with output |
| Total Variable Cost (TVC) | Varies directly with output |
| Total Cost (TC) | TC = TFC + TVC |
| Average Cost (AC or ATC) | AC = TC ÷ Quantity (Q) |
| Marginal Cost (MC) | MC = ΔTC ÷ ΔQ |
| Total Revenue (TR) | TR = Price × Quantity |
| Average Revenue (AR) | AR = TR ÷ Q = Price |
| Marginal Revenue (MR) | MR = ΔTR ÷ ΔQ |
| Profit | Profit = TR − TC |
The profit-maximising rule for firms is to produce where marginal cost equals marginal revenue (MC = MR). At this output level, any further unit would add more to cost than to revenue.
企业的利润最大化法则是生产边际成本等于边际收益 (MC = MR) 的产量。在这一产出水平上，再多生产一单位所增加的成本将超过其带来的收益。
Economies of scale occur when average costs fall as output increases, often due to technical, managerial or financial efficiencies.
规模经济是指随着产量增加平均成本下降，通常源于技术、管理或财务方面的效率提升。
7. Labour Market Indicators | 劳动力市场指标
The labour market is where workers supply their labour and employers demand it. The wage rate is the price of labour.
劳动力市场是工人供给劳动、雇主需求劳动的场所。工资率是劳动的价格。
Key labour market formulas help measure the health of the economy:
关键的劳动力市场公式有助于衡量经济健康状况：
Labour Force = Employed + Unemployed
劳动力 = 就业人数 + 失业人数
Unemployment Rate = (Unemployed ÷ Labour Force) × 100
失业率 = (失业人数 ÷ 劳动力) × 100
Labour Force Participation Rate = (Labour Force ÷ Working-age Population) × 100
劳动力参与率 = (劳动力 ÷ 劳动适龄人口) × 100
Shifts in labour supply can be caused by changes in migration, education levels or the willingness to work. Labour demand shifts when firms’ production needs or productivity change.
劳动供给的移动可能由移民、教育水平或工作意愿的变化引起。当企业的生产需求或生产率变化时，劳动需求会发生移动。
8. Market Failure: Externalities & Public Goods | 市场失灵：外部性与公共物品
Market failure occurs when the free market fails to allocate resources efficiently. Two common causes are externalities and public goods.
当自由市场无法有效配置资源时，就会发生市场失灵。两个常见原因是外部性和公共物品。
A negative externality arises when the production or consumption of a good imposes a cost on third parties not reflected in the price. For example, pollution from a factory creates a social cost greater than the private cost.
负外部性出现在商品的生产或消费对第三方造成成本，且该成本未反映在价格中时。例如，工厂污染造成的社会成本大于私人成本。
A positive externality occurs when third parties receive spillover benefits. An example is education, which benefits society beyond the individual learner.
正外部性发生在第三方获得溢出收益时。例如教育，它使社会受益，而不仅仅是学习者本人。
Public goods are non-excludable and non-rival. Once provided, no one can be excluded from using them, and one person’s use does not reduce availability for others. Street lighting and national defence are classic examples. Private markets often under-provide or fail to provide public goods.
公共物品具有非排他性和非竞争性。一旦提供，就不能阻止任何人使用，且一个人的使用不会减少他人的可用性。路灯和国防是典型例子。私人市场往往提供不足或根本不提供公共物品。
9. Macroeconomic Performance: GDP & Economic Growth | 宏观经济表现：GDP与经济增长
Gross Domestic Product (GDP) measures the total value of all final goods and services produced within a country in a given period. It can be calculated using the expenditure approach:
国内生产总值 (GDP) 衡量一个经济体在一定时期内生产的全部最终商品和服务的总价值。可以使用支出法计算：
GDP = C + I + G + (X − M)
GDP = 消费支出 + 投资支出 + 政府支出 + (出口 − 进口)
Where C is household consumption, I is investment by firms, G is government spending, X is exports and M is imports. Net exports (X − M) capture the impact of trade.
其中 C 代表家庭消费，I 代表企业投资，G 代表政府支出，X 代表出口，M 代表进口。净出口 (X − M) 反映了贸易的影响。
Economic growth is measured by the percentage change in real GDP (adjusted for inflation) over time. A steady increase in real GDP indicates that the economy is expanding.
经济增长通过实际 GDP（剔除通胀因素）随时间的百分比变化来衡量。实际 GDP 的稳步增长表明经济正在扩张。
Economic Growth Rate = ((GDP₂ − GDP₁) ÷ GDP₁) × 100
经济增长率 = ((GDP₂ − GDP₁) ÷ GDP₁) × 100
10. Inflation, Unemployment & Exchange Rates | 通货膨胀、失业与汇率
Inflation is the sustained rise in the general level of prices. It is typically measured using the Consumer Price Index (CPI).
通货膨胀是指物价总水平的持续上升。通常使用消费者价格指数 (CPI) 来衡量。
Inflation Rate = ((CPI in current year − CPI in previous year) ÷ CPI in previous year) × 100
通胀率 = ((当年 CPI − 上年 CPI) ÷ 上年 CPI) × 100
High inflation erodes purchasing power and can create uncertainty. Deflation – a falling general price level – can also be harmful because consumers delay spending.
高通胀侵蚀购买力并可能造成不确定性。通货紧缩——物价总水平下降——同样有害，因为消费者会推迟支出。
Unemployment represents people who are willing and able to work but cannot find a job. The unemployment rate is covered in Section 7; structural, cyclical and frictional are common types.
失业代表那些愿意且有能力工作但找不到工作的人。失业率在第7节已涉及；结构性失业、周期性失业和摩擦性失业是常见的类型。
Exchange rates show the price of one currency in terms of another. If the pound appreciates, UK exports become more expensive for foreign buyers, which may reduce
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