📚 Year 11 WJEC Economics: Formula & Theorem Quick Reference Handbook | Year 11 WJEC 经济：公式定理速查手册
This handbook collects every key formula, elasticity measure and important economic relationship you need for the WJEC Year 11 Economics course. Use it to check your calculations, memorise definitions, and build confidence before the exam. Each section pairs an English explanation with a Chinese explanation so you can master the material bilingually.
本手册汇集了 WJEC Year 11 经济课程所需的每一个关键公式、弹性度量以及重要的经济关系。你可以用它检查计算、记忆定义并在考前建立信心。每个小节都先提供英文解释，再附上中文解释，帮助你用中英双语掌握内容。
1. Price Elasticity of Demand (PED) | 需求价格弹性
PED measures the responsiveness of quantity demanded to a change in the good's own price. The formula is: PED = % change in quantity demanded / % change in price. Always use the percentage change formula: (New - Old)/Old × 100% urves slope downwards, but economists often use the absolute value to describe elasticity.
需求价格弹性（PED）衡量需求量对商品自身价格变化的反应程度。公式为：PED = 需求量变动百分比 / 价格变动百分比。务必使用百分比变动公式：(新值 - 旧值)/旧值 × 100%。PED 通常为负值，因为需求曲线向下倾斜，但经济学家常用其绝对值来描述弹性大小。
If |PED| price cut raises total revenue because the quantity effect outweighs the price effect. If |PED| < 1, demand is price inelastic; a price rise increases total revenue. If |PED| = 1, demand is unit elastic and total revenue stays the same when price changes.
若 |PED| > 1，需求富有价格弹性；降价时，数量效应超过价格效应，因此总收入增加。若 |PED| < 1，需求缺乏价格弹性；提价会使总收入增加。若 |PED| = 1，需求单位弹性，价格变动时总收入保持不变。
on of income spent on the good, whether the good is a luxury or necessity, and the time period considered.
影响 PED 的因素包括替代品的可得性（替代品越多 → 弹性越大）、商品支出占收入的比例、商品属于奢侈品还是必需品，以及考虑的时间长度。
2. Price Elasticity of Supply (PES) | 供给价格弹性
PES captures how much quantity supplied reacts to a price change. The formula is: PES = % change in quantity supplied / % ods that can be produced quickly, or where spare capacity exists, tend to have higher PES.
供给价格弹性（PES）反映供给量对价格变化作出多大反应。公式为：PES = 供给量变动百分比 / 价格变动百分比。由于供给曲线通常向上倾斜，PES 一般为正值。能够快速生产或存在闲置产能的商品往往具有较高的 PES。
If PES > 1, supply is elastic; producers can easily increase output when price rises. If PES < 1, supply is inelastic; producers struggle to expand output quickly. Perfectly inelastic supply has a PES of 0, often seen in fixed-capacity situations (e.g., theatre seats tonight).
若 PES > 1，供给富有弹性，当价格上升时生产者能轻松增加产量。若 PES < 1，供给缺乏弹性，生产者难以迅速扩大产出。完全无弹性供给的 PES 为 0，常见于产能固定的情形（例如今晚的剧院座位数）。
3. Income Elasticity of Demand (YED) | 需求收入弹性
YED indicates how demand changes as consumer income changes. The formula is: YED = % change in quantity demanded / % ED less than 1. Inferior goods have a negative YED because demand falls when income rises.
需求收入弹性（YED）显示需求如何随消费者收入变化。公式为：YED = 需求量变动百分比 / 收入变动百分比。正常商品表现出正的 YED；奢侈品的 YED 通常大于 1，而必需品的 YED 为正但小于 1。低档商品的 YED 为负，因为收入上升时需求下降。
YED helps firms decide which product lines to expand during a boom and which to protect in a recession. It is also used to classify the sectoral pattern of economic growth: as a country gets richer, demand for luxury goods grows faster than for basic goods.
YED 帮助企业决定在繁荣期应扩展哪些产品线，在衰退期又该保护哪些产品。它还用于刻画经济增长中的行业格局：随着一国变得富裕，对奢侈品的需求增长会快于对基本品的需求。
4. Cross Elasticity of Demand (XED) | 需求交叉弹性
the demand for one good responds to a price change of another good. The formula is: XED = % change in quantity demanded of good A / % e), XED is positive; for complements (e.g., printers and ink cartridges), XED is negative.
需求交叉弹性（XED）衡量一种商品的需求对另一种商品价格变化的反应程度。公式为：XED = 商品 A 的需求量变动百分比 / 商品 B 的价格变动百分比。对于替代品（如茶和咖啡），XED 为正；对于互补品（如打印机和墨盒），XED 为负。
The larger the absolute value of XED, the stronger the relationship between the two goods. An XED close to zero suggests the goods are unrelated. XED is especially useful in merger investigations and pricing strategies.
XED 绝对值越大，两种商品之间的关系越强。XED 接近零则表示商品无关。XED 在企业合并调查和定价策略中格外有用。
5. Costs, Revenue and Profit Formulas | 成本、收入与利润公式
rice: AR = P. Marginal revenue (MR) is the extra revenue from selling one more unit: MR = change in TR / change in Q. For a perfectly competitive firm, MR = AR = P. For a monopolist, MR lies below AR.
总收入（TR）是企业从销售中获得的款项：TR = 价格 × 销售数量。平均收入（AR）等于 TR ÷ 数量，也就是价格：AR = P。边际收入（MR）是多卖一单位所带来的额外收入：MR = TR 的变化量 / Q 的变化量。对完全竞争企业而言，MR = AR = P。对垄断企业来说，MR 低于 AR。
(MC) = change in TC / change in Q. Fixed costs do not vary with output (e.g., rent), whereas variable costs do (e.g., raw materials).
总成本（TC）是总固定成本（TFC）和总可变成本（TVC）之和：TC = TFC + TVC。平均成本（AC 或 ATC）= TC / 产量。边际成本（MC）= TC 的变化量 / Q 的变化量。固定成本不随产量变动（如租金），而可变成本会变动（如原材料）。
ortunity cost) from supernormal profit (TR > TC). The shutdown condition is: if price < AVC, the firm minimises loss by stopping production in the short run.
利润为 TR 减去 TC。经济学家区分正常利润（经济利润为零，此时 TR = TC，已将机会成本纳入）和超常利润（TR > TC）。停业条件是：若价格 < AVC，企业在短期内停产可使损失最小化。
6. Profit Maximisation and Efficiency Conditions | 利润最大化与效率条件
C). If MR > MC, the firm should raise output; if MR < MC, it should reduce output. This rule applies to all market structures, though the shapes of MR and MC curves differ.
企业在边际收入等于边际成本（MR = MC）处实现利润最大化。若 MR > MC，应增加产量；若 MR < MC，应减少产量。这一规则适用于所有市场结构，尽管 MR 和 MC 曲线的形状会有所不同。
means resources are allocated exactly in line with consumer preferences. Productive efficiency occurs when firms produce at the lowest point on the average cost curve, i.e., at minimum ATC.
当消费者支付的价格等于生产的边际成本时，即 P = MC，就实现了配置效率。这意味着资源完全按消费者偏好进行配置。生产效率发生在企业于平均成本曲线最低点生产时，即在最小 ATC 处。
7. Macroeconomic Indicators – GDP, Unemployment, Inflation | 宏观经济指标——GDP、失业与通胀
g: GDP = C + I + G + (X − M), where C is consumption, I is investment, G is government spending, X is exports and M is imports. The income approach totals wages, profits, rents and other factor incomes earned within the economy.
国内生产总值（GDP）衡量一国在一年内生产的总产出价值。支出法将所有支出加总：GDP = C + I + G + (X − M)，其中 C 为消费，I 为投资，G 为政府支出，X 为出口，M 为进口。收入法则将国内赚取的工资、利润、租金和其他要素收入加总。
The unemployment rate is calculated as: (Number of unemployed / Labour force) × 100% easures; the WJEC specification expects students to know the formula and interpret trends.
失业率按下式计算：(失业人数 / 劳动力) × 100%。劳动力包括就业人口加上正在积极寻找工作的人口。英国的两种主要测量方法是申请人数统计和 ILO 劳动力调查；WJEC 考纲要求学生掌握公式并能够解读趋势。
is: Inflation rate = (CPI in current year − CPI in previous year) / CPI in previous year × 100%. Deflation occurs when this rate is negative.
通货膨胀衡量一般物价水平的持续上升。消费者价格指数（CPI）是主要指标。通胀率公式为：通胀率 = (今年 CPI − 去年 CPI) / 去年 CPI × 100%。该比率为负时出现通货紧缩。
8. The Multiplier Effect | 乘数效应
ltiplier (k). The simple closed-economy multiplier is: k = 1 / (1 − MPC) or k = 1 / MPS, where MPC is the marginal propensity to consume and MPS is the marginal propensity to save (MPC + MPS = 1).
一笔初始的支出注入经济体后，可能带来国民收入更大幅度的最终增长。这一效应的规模由乘数（k）体现。简单的封闭经济乘数为：k = 1 / (1 − MPC) 或 k = 1 / MPS，其中 MPC 为边际消费倾向，MPS 为边际储蓄倾向（MPC + MPS = 1）。
If the government increases spending by £ nd the MPC is 0.8, the multiplier is 1/(1−0.8) = 5, so national income could rise by up to £ pen economy with taxation and imports, the multiplier will be smaller because of leakages.
如果政府增加支出 100 亿英镑，且 MPC 为 0.8，则乘数为 1/(1−0.8)=5，因此国民收入最多可增加 500 亿英镑。在一个存在税收和进口的更开放的经济中，由于漏出效应，乘数会更小。
9. Exchange Rates and Balance of Payments | 汇率与国际收支
An exchange rate is the price of one currency in terms of another. The value of a currency can appreciate (stronger) or depreciate (weaker). An appreciation makes exports more expensive and imports cheaper, worsening the trade balance in the short run, while a depreciation does the opposite – this relationship is summarised by the J-curve effect.
汇率是一种货币用另一种货币表示的价格。货币价值可以升值（走强）或贬值（走弱）。升值会使出口变贵、进口变便宜，短期内恶化贸易差额；贬值则起相反作用——这一关系由 J 曲线效应概括。
The current account of the balance of payments records trade in goods and services (X − M), plus primary and secondary income flows. A current account deficit means a country is spending more on imports and income outflows than it earns from exports and inflows. WJEC expects students to use numerical examples: convert prices using a given exchange rate and calculate the change in the current account balance.
国际收支中的经常账户记录商品和服务贸易（X − M）以及初次收入与二次收入流动。经常账户赤字意味着一国在进口和收入流出上的支出超过了它从出口和流入中获得的收入。WJEC 要求学生能运用数值例子：按给定汇率换算价格，并计算经常账户余额的变化。
10. Comparative Advantage and Terms of Trade | 比较优势与贸易条件
The law of comparative advantage states that countries should specialise in goods where they have the lowest opportunity cost, rather than the lowest absolute cost. The opportunity cost of producing one unit of good A is the amount of good B that must be given up. Even if one country is more efficient in everything, both can gain from trade by specialising according to their comparative advantage.
比较优势法则指出，各国应该专门生产机会成本最低的商品，而不是绝对成本最低的商品。生产一单位商品 A 的机会成本就是必须放弃的商品 B 的数量。即便某个国家在所有领域都更高效，两国也能通过按比较优势进行专业化生产而从贸易中获益。
improvement (a rise) means a country can buy more imports with a given volume of exports. A deterioration means it must export more to afford the same imports. Students should be able to calculate and interpret simple terms of trade figures.
贸易条件指数衡量出口相对于进口的价格：贸易条件 = (出口价格指数 / 进口价格指数) × 100。贸易条件改善（数值上升）意味着用给定数量的出口可以买到更多的进口。恶化则意味着必须出口更多才能负担同等进口。学生应能计算并解读简单的贸易条件数据。
11. Labour Market and Wage Determination | 劳动力市场与工资决定
al revenue product of labour: MRP = MPL × MR, where MPL is the marginal physical product of labour. A profit-maximising firm hires workers up to the point where MRP = wage rate.
在竞争性劳动力市场中，工资由劳动力的需求与供给相等处决定。劳动力需求来自劳动的边际收入产品：MRP = MPL × MR，其中 MPL 为劳动的边际实物产品。利润最大化的企业会持续雇佣工人，直至 MRP = 工资率。
Supply of labour depends on the size of the working population, the wage rate, non-wage factors (e.g., working conditions), and barriers to entry such as qualifications. Government interventions, like the National Minimum Wage, create a wage floor above the equilibrium. Students should analyse the impact of a minimum wage using a labour market diagram and numerical data.
劳动力供给取决于劳动人口规模、工资水平、非工资因素（如工作条件）以及资格要求等进入壁垒。政府干预措施，如国民最低工资，会设定一个高于均衡水平的工资下限。学生应能运用劳动力市场图示和数字数据分析最低工资的影响。
12. Market Failure and Government Intervention Formulas | 市场失灵与政府干预公式
Market failure occurs when the free market fails to achieve allocative efficiency, often because of externalities. A negative externality means social cost > private cost; a positive externality means social benefit > private benefit. The welfare loss (deadweight loss) can be visualised as a triangle between the marginal social cost and marginal social benefit curves.
当自由市场无法实现配置效率时，就会出现市场失灵，原因往往是外部性。负外部性意味着社会成本 > 私人成本；正外部性意味着社会收益 > 私人收益。福利损失（无谓损失）可在边际社会成本和边际社会收益曲线之间用三角形表示出来。
mand and supply. The tax burden is shared between consumers and producers; the more inelastic side bears more of the burden. The formula for tax incidence on consumers: (PES / (PES + |PED|)) × tax per unit.
政府使用间接税将负外部性内部化。价格上升幅度取决于每单位税额以及供需弹性。税负由消费者和生产者分担；越是缺乏弹性的一方承担的税负越重。消费者承担的税负比例公式为：(PES / (PES + |PED|)) × 每单位税额。
on and shift the supply curve to the right. The subsidy per unit shared by producers is based on a similar formula: (|PED| / (PES + |PED| nts may be asked to calculate new equilibrium prices and government spending on subsidies.
补贴降低生产成本，使供给曲线右移。生产者得到的每单位补贴份额可按类似公式计算：(|PED| / (PES + |PED|)) × 每单位补贴额。WJEC 考生可能需计算新的均衡价格以及政府的补贴总支出。
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