📚 GCSE WJEC Economics: Formula Summary Handbook | GCSE WJEC 经济：公式汇总手册
Mastering the key calculations in WJEC GCSE Economics gives you the power to interpret data, predict market reactions, and evaluate policy outcomes with precision. This handbook brings together every essential formula—from elasticity to macroeconomic indicators—forming a one-stop revision aid for both Unit 1 and Unit 2. Use it alongside past papers to build speed and confidence in numerical application.
掌握 WJEC GCSE 经济学中的关键计算，能让你精准解读数据、预测市场反应并评估政策效果。本手册汇总了从弹性到宏观经济指标的每一项核心公式，是涵盖第一单元与第二单元的综合复习工具。搭配历年真题使用，可帮助你提升计算速度与答题信心。
1. Price Elasticity of Demand (PED) | 需求的价格弹性
Price elasticity of demand measures how much the quantity demanded of a product changes in response to a change in its own price. The coefficient indicates whether demand is elastic, inelastic, or unitary.
需求的价格弹性衡量需求量对自身价格变化的反应程度。该系数表明需求是富有弹性、缺乏弹性还是单位弹性。
PED = (%Δ quantity demanded) / (%Δ price)
Percentage change can be calculated using the formula: %Δ = [(New value - Original value) / Original value] × 100.
百分比变化的计算方式为：%Δ = [(新值 - 原值) / 原值] × 100。
- Interpretation: ice elastic; if PED < 1, demand is price inelastic; if PED = 1, demand is unit elastic.
- 解读：若 PED > 1，需求富有价格弹性；若 PED < 1，需求缺乏价格弹性；若 PED = 1，需求为单位弹性。
- Revenue rule: When demand is elastic, lowering price increases total revenue; when inelastic, raising price increases total revenue.
- 收益法则：当需求富有弹性时，降价可增加总收入；当需求缺乏弹性时，提价可增加总收入。
2. Income Elasticity of Demand (YED) | 需求的收入弹性
YED captures the sensitivity of demand to changes in consumer incomes. It helps classify goods as normal, luxury, or inferior.
YED 反映需求对消费者收入变化的敏感程度，可用于区分正常品、奢侈品和低档品。
YED = (%Δ quantity demanded) / (%Δ income)
A positive YED signals a normal good; if YED > 1, it is a luxury good. A negative YED identifies an inferior good.
正的 YED 表示正常品；若 YED > 1，则为奢侈品。负的 YED 则为低档品。
- Firms use YED to forecast sales during economic booms or recessions.
- 企业利用 YED 预测经济繁荣或衰退期间的销售情况。
3. Cross Elasticity of Demand (XED) | 需求的交叉弹性
XED measures the responsiveness of the quantity demanded for one good when the price of another good changes. It reveals whether goods are substitutes or complements.
XED 衡量一种商品的需求量对另一种商品价格变化的反应程度，揭示商品之间是替代品还是互补品。
XED = (%Δ quantity demanded of Good A) / (%Δ price of Good B)
Substitutes have a positive XED (e.g. tea and coffee); complements have a negative XED (e.g. printers and ink cartridges). An XED close to zero suggests unrelated goods.
替代品的 XED 为正（如茶与咖啡）；互补品的 XED 为负（如打印机与墨盒）。XED 接近零表明商品不相关。
- Business strategy: A retailer can predict how a competitor's price cut might affect its own product sales.
- 商业策略：零售商可预测竞争对手降价对本企业产品销售的影响。
4. Price Elasticity of Supply (PES) | 供给的价格弹性
PES indicates how readily producers can change the quantity supplied in response to a price change. It depends on factors like spare capacity, time period, and stock levels.
PES 反映生产者对价格变化调整供给量的能力，取决于闲置产能、时间长短和库存水平等因素。
PES = (%Δ quantity supplied) / (%Δ price)
If PES > 1, supply is elastic—firms can quickly increase output. If PES < 1, supply is inelastic—output is slow to adjust. A PES of zero means perfectly inelastic supply.
若 PES > 1，供给富有弹性——企业能迅速增产；若 PES < 1，供给缺乏弹性——产出调整缓慢。PES 为 0 表示完全无弹性供给。
5. Costs, Revenue and Profit | 成本、收益与利润
Understanding how costs and revenue interact is essential for profit maximisation. These formulas help compute total, average, and per-unit measures.
理解成本与收益的相互作用对利润最大化至关重要。以下公式可计算总量、平均数和单位指标。
Total Cost (TC) = Total Fixed Cost (TFC) + Total Variable Cost (TVC)
Average Total Cost (ATC) = TC / Quantity (Q)
Total Revenue (TR) = Price (P) × Quantity (Q)
Profit = TR − TC
Fixed costs remain constant regardless of output (e.g. rent); variable costs change with production (e.g. raw materials). When TR exceeds TC, the firm makes a profit; when TC exceeds TR, it makes a loss.
固定成本不随产量变化（如租金）；可变成本随生产变化（如原材料）。当 TR 大于 TC 时，企业盈利；当 TC 大于 TR 时，企业亏损。
- consider marginal cost (MC) and marginal revenue (MR): profit is maximised where MC = MR.
- 企业同时关注边际成本 (MC) 与边际收益 (MR)：当 MC = MR 时利润实现最大化。
6. Break-even Analysis | 盈亏平衡分析
Break-even analysis identifies the output level at which total revenue equals total costs, meaning neither profit nor loss is made. It is a vital planning tool for start-ups.
盈亏平衡分析确定总收入等于总成本的产出水平，即既不盈利也不亏损。这是初创企业重要的规划工具。
Break-even output = TFC / (Selling price per unit − Variable cost per unit)
The denominator is the contribution per unit—the amount each unit sold contributes towards covering fixed costs. Beyond the break-even point, each additional unit sold generates profit.
分母为单位贡献毛益——每售出一单位产品对覆盖固定成本的贡献。超过盈亏平衡点后，每多售出一单位产品即可产生利润。
- = Actual sales − Break-even sales. It shows how much sales can fall before a loss occurs.
- 安全边际 = 实际销量 − 盈亏平衡销量，反映销量下降多少才会出现亏损。
7. Labour Productivity and Average Costs | 劳动生产率与平均成本
Labour productivity measures output per worker or per hour worked and directly impacts a firm's average costs. Higher productivity usually reduces cost per unit.
劳动生产率衡量每位工人或每小时的产出，直接影响企业的平均成本。生产率提升通常会降低单位成本。
Labour productivity = Total output / Number of workers (or hours worked)
When productivity rises, the same input yields more output, so ATC tends to fall. This can give a company a competitive advantage by allowing lower prices or higher margins.
当生产率提升时，同等投入产出更多，因此 ATC 趋于下降。这可使企业通过降低售价或提高利润率获得竞争优势。
- Firms may invest in training, better equipment, or technology to boost productivity.
- 企业可通过培训、购置更好的设备或技术来提升生产率。
8. Unemployment and Labour Market Indicators | 失业与劳动力市场指标
The unemployment rate is the most widely used measure of labour market slack. It compares the number of people actively seeking work to the total labour force.
失业率是衡量劳动力市场闲置程度最常用的指标，它比较了积极求职人数与劳动力总人口。
Unemployment rate = (Number of unemployed / Labour force) × 100
The labour force includes all people of working age who are either employed or actively looking for work. Students, retirees, and discouraged workers are excluded.
劳动力包括所有处于工作年龄且已就业或正在积极寻找工作的人。学生、退休人员和丧失信心的劳动者不纳入统计。
- age population) × 100; participation rate = (Labour force / Working-age population) × 100.
- 其他实用指标：就业率 = (就业人数 / 劳动年龄人口) × 100；劳动参与率 = (劳动力 / 劳动年龄人口) × 100。
9. Inflation and the Consumer Price Index | 通货膨胀与消费者价格指数
Inflation tracks the general rise in the price level over time. The Consumer Price Index (CPI) is the UK's main measure, and the inflation rate is derived from its percentage change.
通货膨胀追踪物价总水平随时间上涨的趋势。消费者价格指数 (CPI) 是英国的主要衡量指标，通胀率由其百分比变动得出。
Inflation rate = [(CPI current year − CPI previous year) / CPI previous year] × 100
A low and stable inflation rate is a government objective (2% target in the UK). High inflation erodes purchasing power, while deflation can discourage spending.
低且稳定的通胀率是政府目标（英国设为 2%）。高通胀侵蚀购买力，而通货紧缩可能抑制支出。
- CPI basket weights are updated annually to reflect typical household spending patterns.
- CPI 篮子的权重每年更新，以反映典型家庭的消费模式。
10. GDP and Economic Growth | 国内生产总值与经济增长
Gross Domestic Product (GDP) measures the total value of all goods and services produced in a country over a given period. Economic growth is the increase in real GDP over time.
国内生产总值 (GDP) 衡量一个国家在特定时期内生产的所有最终商品与服务的总价值。经济增长是实际 GDP 随着时间的推移而增加。
Nominal GDP = Σ (Price × Quantity) for all final goods and services
Real GDP = (Nominal GDP / GDP deflator) × 100
Economic growth rate = [(Real GDP year 2 − Real GDP year 1) / Real GDP year 1] × 100
GDP per capita = Real GDP / Population
Using real GDP strips out the effect of inflation, giving a truer picture of output changes. GDP per capita is a rough indicator of living standards.
采用实际 GDP 剔除通胀影响，能更真实地反映产出变化。人均 GDP 是衡量生活水平的粗略指标。
11. International Trade and Exchange Rates | 国际贸易与汇率
The balance of trade records the difference between visible exports and visible imports. Exchange rate formulas are essential for converting prices and understanding currency movements.
贸易差额记录有形出口与有形进口之间的差值。汇率公式对于价格换算和理解货币波动不可或缺。
Balance of trade = Value of exports − Value of imports
When given an exchange rate, e.g. £1 = $1.30, you can convert amounts using:
当给定汇率，如 £1 = $1.30 时，可用以下方式换算：
Amount in foreign currency = Amount in home currency × Exchange rate
If the pound appreciates, UK exports become more expensive and imports cheaper; if it depreciates, exports become cheaper and imports more expensive.
若英镑升值，英国出口变贵、进口变便宜；若英镑贬值，出口变便宜、进口变贵。
- Appreciation means £1 buys more foreign currency; depreciation means £1 buys less.
- 升值意味着 £1 可兑换更多外币；贬值意味着 £1 兑换更少外币。
12. Taxation and Disposable Income | 税收与可支配收入
Taxation reduces consumers' disposable income and affects spending. Key formulas involve income tax, National Insurance, and the calculation of disposable income.
税收减少消费者的可支配收入并影响支出。关键公式涉及个人所得税、国民保险金以及可支配收入的计算。
isposable income = Gross income − Income tax − National Insurance contributions + Benefits
The UK uses a progressive income tax system: higher earnings are taxed at higher marginal rates. The average tax rate can be calculated as total tax divided by gross income.
英国实行累进所得税制度：高收入适用更高的边际税率。平均税率可计算为总税额除以总收入。
- Average tax rate = (Total tax paid / Gross income) × 100.
- 平均税率 = (已缴总税额 / 总收入) × 100。
- Indirect taxes such as VAT are levied as a percentage of spending and are not shown directly in disposable income calculations but affect real purchasing power.
- 增值税等间接税按支出的百分比征收，虽不直接纳入可支配收入计算，但影响实际购买力。
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