📚 IGCSE CIE Economics: Formula Handbook | IGCSE CIE 经济：公式汇总手册
This handbook collects the essential formulas required for the CIE IGCSE Economics (0455) syllabus. For each formula you will find a clear definition, a step‑by‑step explanation of how it is calculated, and what the result means in exam contexts. Being comfortable with these equations will not only support your calculation questions but also help you analyse data, evaluate policies and build stronger essay arguments.
本手册汇集了 CIE IGCSE 经济（0455）考试所需的全部核心公式。每个公式都配有清晰的定义、逐步计算说明以及在考试中的实际用途。熟练掌握这些方程不仅能帮你解决计算题，还能让你更自信地分析数据、评估政策，并为论文题构建有力论证。
1. Price Elasticity of Demand (PED) | 需求价格弹性
Price elasticity of demand measures the responsiveness of quantity demanded to a change in the good’s own price. It is always negative due to the law of demand, but economists usually ignore the minus sign and focus on absolute value.
需求价格弹性衡量需求量对商品自身价格变动的反应程度。由于需求定律，该值始终为负数，但经济学家通常忽略负号，只关注绝对值。
PED = % change in quantity demanded ÷ % change in price
Where % change = (new value − original value) ÷ original value × 100. If PED > 1, demand is price elastic; if PED < 1, demand is price inelastic; if PED = 1, demand is unit elastic.
其中百分比变化 = （新数值 − 原始数值） ÷ 原始数值 × 100。若 PED > 1，需求富有弹性；PED < 1，需求缺乏弹性；PED = 1，需求单位弹性。
2. Price Elasticity of Supply (PES) | 供给价格弹性
Price elasticity of supply shows how much the quantity supplied of a good changes when its price changes. Unlike PED, PES is usually positive because higher prices encourage firms to supply more.
供给价格弹性反映商品价格变动时供给量变化的程度。与 PED 不同，PES 通常为正值，因为价格上涨会激励企业增加供给。
PES = % change in quantity supplied ÷ % change in price
The value of PES indicates how easily producers can expand output. A PES greater than 1 means supply is elastic; less than 1 means supply is inelastic.
PES 的数值表明生产者扩大产出的难易程度。PES 大于 1 表示供给富有弹性，小于 1 表示供给缺乏弹性。
3. Income Elasticity of Demand (YED) | 需求收入弹性
Income elasticity of demand measures how quantity demanded responds to a change in consumers’ income. It helps classify goods as normal or inferior.
需求收入弹性衡量需求量对消费者收入变动的反应程度，可用于区分正常品与低档品。
YED = % change in quantity demanded ÷ % change in income
If YED is positive, the good is a normal good (and if YED > 1, it is a luxury). If YED is negative, the good is an inferior good.
YED 为正，该商品为正常品（若 YED > 1 则为奢侈品）；YED 为负，该商品为低档品。
4. Cross Elasticity of Demand (XED) | 需求交叉弹性
Cross elasticity of demand measures the responsiveness of demand for one good (A) when the price of another good (B) changes. It identifies substitutes and complements.
需求交叉弹性衡量一种商品（A）的需求量对另一种商品（B）价格变动的反应程度，用于识别替代品与互补品。
XED = % change in quantity demanded of good A ÷ % change in price of good B
XED is positive for substitutes and negative for complements. The larger the absolute value, the stronger the relationship.
替代品的 XED 为正，互补品的 XED 为负。绝对值越大，关系越强。
5. Costs, Revenue and Profit | 成本、收入与利润
Firms need to understand their costs and revenues to decide on output levels. These formulas are fundamental for profit maximisation and break‑even analysis.
企业需要了解成本与收入才能决定产量。这些公式是利润最大化和盈亏平衡分析的基础。
Total Cost (TC) = Total Fixed Cost (TFC) + Total Variable Cost (TVC)
总成本 = 总固定成本 + 总可变成本
Average Cost (AC) = TC ÷ Quantity (Q)
平均成本 = 总成本 ÷ 产量
Average Fixed Cost (AFC) = TFC ÷ Q
平均固定成本 = 总固定成本 ÷ 产量
Average Variable Cost (AVC) = TVC ÷ Q
平均可变成本 = 总可变成本 ÷ 产量
Marginal Cost (MC) = Change in TC ÷ Change in Q
边际成本 = 总成本变化量 ÷ 产量变化量
Total Revenue (TR) = Price (P) × Q
总收入 = 价格 × 销量
Average Revenue (AR) = TR ÷ Q = P
平均收入 = 总收入 ÷ 销量 = 价格
Profit = TR − TC
利润 = 总收入 − 总成本
These equations appear frequently in data‑response questions. Remember that profit‑maximising output occurs where MC = MR, and a firm breaks even when TR = TC.
这些公式在数据分析题中经常出现。记住，利润最大化产量出现在 MC = MR 处，企业盈亏平衡时 TR = TC。
6. Productivity | 生产率
Productivity measures how efficiently inputs are being turned into output. Higher productivity lowers average costs and can improve living standards.
生产率衡量投入转化为产出的效率。生产率提高能降低平均成本并提升生活水平。
Labour Productivity = Total Output ÷ Number of Workers (or Labour Hours)
劳动生产率 = 总产出 ÷ 工人数（或劳动小时数）
Capital Productivity = Output ÷ Units of Capital
资本生产率 = 产出 ÷ 资本单位数
In IGCSE papers you may be asked to calculate output per worker or to explain the link between productivity, costs and international competitiveness.
在 IGCSE 试卷中，你可能会被要求计算人均产出，或解释生产率、成本与国际竞争力之间的关系。
7. Unemployment Rate | 失业率
The unemployment rate is a key macroeconomic indicator. It tells us the percentage of the labour force that is actively seeking work but cannot find employment.
失业率是关键的宏观经济指标，表示劳动力中正在积极寻找工作但未能就业的人口百分比。
Unemployment Rate = (Number of Unemployed ÷ Labour Force) × 100
失业率 = （失业人数 ÷ 劳动力总数） × 100
Where the labour force = employed + unemployed. Students often confuse the labour force with the whole population; always check that you use the economically active group.
劳动力 = 就业者 + 失业者。学生常将劳动力与总人口混淆；务必使用经济活动人口计算。
8. Inflation Rate (Consumer Price Index) | 通货膨胀率（消费者价格指数）
Inflation is the sustained increase in the general price level. The most common measure is the Consumer Price Index (CPI).
通货膨胀是指整体物价水平的持续上涨。最常用的衡量指标是消费者价格指数（CPI）。
Inflation Rate = (CPI₁ − CPI₀) ÷ CPI₀ × 100
通货膨胀率 = （本年 CPI − 上年 CPI） ÷ 上年 CPI × 100
In exam questions you may be given a weighted basket of goods and need to construct a simple price index before calculating the inflation rate. Always express your final answer as a percentage.
考试中可能会给出一个加权商品篮，要求你先构建一个简单的价格指数，再计算通胀率。最终答案必须用百分数表示。
9. Gross Domestic Product (GDP) | 国内生产总值
GDP measures the total value of goods and services produced in a country over a period. For meaningful comparisons, economists use real GDP and GDP per capita.
GDP 衡量一国在一定时期内生产的全部最终商品与服务的总价值。为进行有意义的比较，经济学家使用实际 GDP 和人均 GDP。
Real GDP = (Nominal GDP ÷ Price Index) × 100
实际 GDP = （名义 GDP ÷ 价格指数） × 100
GDP per Capita = Real GDP ÷ Total Population
人均 GDP = 实际 GDP ÷ 总人口
Real GDP removes the effect of inflation, allowing you to compare output over time. GDP per capita gives a rough indication of average living standards, but it does not show income distribution.
实际 GDP 剔除了通胀影响，便于跨时期比较产出。人均 GDP 可粗略反映平均生活水平，但无法显示收入分配状况。
10. Exchange Rates | 汇率
Exchange rates express the value of one currency in terms of another. A change in the exchange rate can be calculated as a percentage appreciation or depreciation.
汇率表示一种货币用另一种货币计价的价值。汇率变动可以计算为货币升值或贬值的百分比。
% Change = (New Exchange Rate − Old Exchange Rate) ÷ Old Exchange Rate × 100
汇率变动百分比 = （新汇率 − 旧汇率） ÷ 旧汇率 × 100
A positive result means the domestic currency has appreciated; a negative result means it has depreciated. Be careful to specify which currency you are analysing.
结果为正值表示本币升值，负值表示本币贬值。注意明确你分析的是哪一种货币。
11. Taxation | 税收
Governments use taxes to raise revenue and influence behaviour. In IGCSE Economics, you might need to calculate tax revenue per unit and total tax revenue, as well as the tax burden on consumers and producers.
政府利用税收筹集收入并影响行为。在 IGCSE 经济中，你可能需要计算单位税额、总税收收入，以及消费者和生产者的税收负担。
Tax per unit = Post‑tax price − Price received by producers
单位税额 = 税后价格 − 生产者实际获得的价格
Total Tax Revenue = Tax per unit × Post‑tax quantity
总税收收入 = 单位税额 × 税后销售量
Consumer Burden = (Post‑tax price − Pre‑tax equilibrium price) × Post‑tax quantity
消费者负担 = （税后价格 − 税前均衡价格） × 税后销售量
Producer Burden = (Pre‑tax equilibrium price − Price received by producers) × Post‑tax quantity
生产者负担 = （税前均衡价格 − 生产者实际价格） × 税后销售量
These calculations help explain the incidence of indirect taxes. The more inelastic the demand or supply, the greater the share of the tax that side bears.
这些计算有助于解释间接税的归宿。需求或供给越缺乏弹性，该方承担的税收份额就越大。
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