📚 IGCSE Economics: Formula Summary Handbook | IGCSE 经济：公式汇总手册
This handbook brings together all the essential formulae you need for IGCSE Economics. From elasticities to costs, revenue, productivity and key macroeconomic indicators, these equations form the quantitative backbone of the syllabus. Mastering them will not only boost your confidence in calculations but also deepen your understanding of economic relationships.
本手册汇总了 IGCSE 经济课程中所有核心公式。从弹性到成本、收益、生产率以及关键的宏观经济指标，这些方程式构成了教学大纲的定量基础。熟练掌握它们不仅能增强你计算的信心，还能加深你对经济关系的理解。
1. Price Elasticity of Demand (PED) | 需求价格弹性
PED = %ΔQd ÷ %ΔP
ts of measurement issues. If PED > 1, demand is elastic; if PED < 1, demand is inelastic; and if PED = 1, demand is unit elastic.
需求价格弹性衡量需求量对价格变化的反应程度。该公式采用百分比变化以避免计量单位问题。如果 PED > 1，需求富有弹性；如果 PED < 1，需求缺乏弹性；如果 PED = 1，需求为单位弹性。
You may also see the formula expressed as: (ΔQd / Qd) ÷ (ΔP / P). Remember to take absolute values, since PED is usually treated as a positive number even though demand curves slope downward.
你也会看到此公式表达为：(ΔQd / Qd) ÷ (ΔP / P)。记住取绝对值，因为尽管需求曲线向下倾斜，PED 通常被视为正数。
2. Price Elasticity of Supply (PES) | 供给价格弹性
PES = %ΔQs ÷ %ΔP
Price elasticity of supply shows how much the quantity supplied changes when price changes. It is always positive because the supply curve slopes upward. A value greater than 1 indicates elastic supply, while less than 1 indicates inelastic supply.
供给价格弹性显示当价格变化时供给量变化多少。由于供给曲线向上倾斜，该值总是为正。数值大于 1 表示供给富有弹性，小于 1 表示供给缺乏弹性。
Key determinants of PES include time period, spare production capacity, and ease of storing inventory. The longer the time producers have to adjust, the more elastic supply becomes.
PES 的关键决定因素包括时间周期、闲置生产能力和库存存储的难易程度。生产者调整时间越长，供给就会变得越富有弹性。
3. Income Elasticity of Demand (YED) | 需求收入弹性
YED = %ΔQd ÷ %ΔIncome
Income elasticity of demand measures how quantity demanded responds to changes in consumer income. For normal goods, YED is positive; for inferior goods, YED is negative. Within normal goods, those with YED > 1 are luxury goods, while those with 0 < YED < 1 are necessities.
需求收入弹性衡量需求量如何随消费者收入变化而变动。对于正常商品，YED 为正；对于低档商品，YED 为负。在正常商品中，YED > 1 的是奢侈品，0 < YED < 1 的是必需品。
Understanding YED helps firms forecast demand as the economy grows. A negative YED signals an inferior good, such as own-brand basic groceries or bus travel.
理解 YED 有助于企业在经济增长时预测需求。负的 YED 标志着低档商品，例如自有品牌基础食品杂货或公交车出行。
4. Cross Elasticity of Demand (XED) | 需求交叉弹性
XED = %ΔQd of Good A ÷ %ΔP of Good B
Cross elasticity of demand indicates the relationship between two goods. A positive XED implies substitutes (e.g., tea and coffee), because a rise in the price of Good B increases quantity demanded of Good A. A negative XED implies complements (e.g., printers and ink cartridges), as a price rise for Good B reduces demand for Good A.
需求交叉弹性显示了两种商品之间的关系。正的 XED 意味着替代品（如茶与咖啡），因为商品 B 的价格上升会增加对商品 A 的需求量。负的 XED 意味着互补品（如打印机与墨盒），因为商品 B 的价格上升会减少对商品 A 的需求。
An XED close to zero suggests the two goods are unrelated. The strength of the relationship is important for pricing strategies and merger analysis.
XED 接近零表明两种商品不相关。这种关系的强度对于定价策略和并购分析很重要。
5. Total, Average and Marginal Revenue | 总收益、平均收益与边际收益
TR = P × Q
AR = TR ÷ Q = P
MR = ΔTR ÷ ΔQ
Total revenue is the money a firm receives from selling its output. Average revenue is simply the price per unit, because TR/Q equals price. Marginal revenue is the extra revenue from selling one additional unit. Under perfect competition, MR equals AR and price. For a monopolist, MR lies below AR.
总收益是企业出售产出所获得的资金。平均收益就是单位价格，因为 TR/Q 等于价格。边际收益是出售额外一单位产品所带来的额外收益。在完全竞争下，MR 等于 AR 也等于价格。对于垄断者，MR 低于 AR。
ue concepts allows firms to identify where revenue is maximised, which occurs when MR = 0.
理解这些收益概念有助于企业确定收益最大化的点，即 MR = 0 时。
6. Total Cost, Average Cost and Marginal Cost | 总成本、平均成本与边际成本
TC = TFC + TVC
AFC = TFC ÷ Q
AVC = TVC ÷ Q
ATC (or AC) = TC ÷ Q = AFC + AVC
MC = ΔTC ÷ ΔQ
Total cost is divided into total fixed cost (independent of output) and total variable cost (changes with output). Average fixed cost falls continuously as output rises. The average total cost curve is U-shaped due to spreading fixed costs initially and later diminishing returns. Marginal cost is the extra cost of producing one more unit; it cuts ATC and AVC at their lowest points.
总成本分为总固定成本（与产出无关）和总可变成本（随产出变动）。平均固定成本随着产出增加持续下降。平均总成本曲线呈 U 形，因为初期分摊固定成本后阶段边际回报递减。边际成本是多生产一单位产品的额外成本；它穿过 ATC 和 AVC 的最低点。
These cost structures underpin a firm's supply decisions and break-even analysis.
这些成本结构支撑着企业的供给决策和盈亏平衡分析。
7. Profit Maximisation Condition | 利润最大化条件
Profit = TR – TC
Profit is maximised where MR = MC
Accounting profit is simply total revenue minus total cost. However, the profit-maximising level of output occurs at the quantity where marginal revenue equals marginal cost. If MR > MC, the firm should increase output; if MR < MC, it should reduce output. This rule applies to all firms regardless of market structure.
会计利润就是总收益减去总成本。然而，利润最大化的产出水平出现在边际收益等于边际成本的数量上。如果 MR > MC，企业应增加产出；如果 MR < MC，则应减少产出。这一规则适用于所有企业，无论市场结构如何。
between TR and TC reaches its maximum. Normal profit occurs when TR = TC (i.e., AR = AC).
在利润最大化产出下，TR 与 TC 之间的差距达到最大。当 TR = TC（即 AR = AC）时，企业获得正常利润。
8. Break-even Point | 盈亏平衡点
Break-even output (units) = TFC ÷ (Price – AVC)
At break-even: TR = TC
The break-even point is where total revenue covers total costs exactly, yielding zero economic profit. The formula using contribution per unit (price minus average variable cost) tells the firm how many units it must sell to cover all fixed costs. Above this output, each additional unit sold adds to profit.
盈亏平衡点是总收益恰好覆盖总成本、经济利润为零的点。使用单件贡献（价格减平均可变成本）的公式告诉企业必须售出多少单位才能弥补所有固定成本。高于这一产出，每多卖一件就增加利润。
Break-even analysis is crucial for start-ups and risk assessment. A lower break-even output means lower risk.
盈亏平衡分析对初创企业和风险评估至关重要。盈亏平衡产出越低，风险越小。
9. Productivity | 生产率
Labour productivity = Total output ÷ Number of workers
Capital productivity = Total output ÷ Units of capital
Productivity measures the efficiency of input use. Higher labour productivity means each worker produces more, which can lower average costs and improve living standards. Improvements come from better technology, training, and specialisation.
生产率衡量投入使用的效率。更高的劳动生产率意味着每位工人的产量更多，这能降低平均成本并提高生活水平。改进来自更好的技术、培训和专业化。
While labour productivity is the most common measure, capital productivity is also relevant for manufacturing and technology-heavy sectors.
尽管劳动生产率为最常见指标，资本生产率在制造业和技术密集型行业也同样重要。
10. Unemployment Rate | 失业率
Unemployment rate = (Number of unemployed ÷ Labour force) × 100
The labour force includes those employed and those actively seeking work. The unemployment rate is a key indicator of economic health. Economists distinguish between frictional, structural, cyclical, and seasonal unemployment. A rising unemployment rate typically signals a slack in the economy.
劳动力包括就业人员和积极寻找工作的人员。失业率是经济健康的一个关键指标。经济学家区分摩擦性失业、结构性失业、周期性失业和季节性失业。失业率上升通常表明经济疲软。
Full employment does not mean zero unemployment; it implies only frictional and structural unemployment exist (the natural rate of unemployment).
充分就业并不意味着零失业率；它只意味着存在摩擦性失业和结构性失业（自然失业率）。
11. Inflation Rate (CPI) | 通货膨胀率 (消费者价格指数)
Inflation rate = [(CPI current year – CPI previous year) ÷ CPI previous year] × 100
The Consumer Price Index (CPI) tracks the average price of a basket of goods and services. The inflation rate measures the percentage increase in the general price level. High inflation erodes purchasing power; deflation (negative inflation) can be equally damaging if sustained.
消费者价格指数（CPI）追踪一篮子商品和服务的平均价格。通货膨胀率衡量一般物价水平的百分比涨幅。高通胀侵蚀购买力；持续的通缩同样可能造成损害。
Alternative measures include the Retail Price Index (RPI). Central banks target a low and stable inflation rate, typically around 2%.
替代指标包括零售价格指数（RPI）。中央银行通常将低而稳定的通胀率定为目标，大约在 2% 左右。
12. Economic Growth Rate | 经济增长率
Real GDP growth rate = [(Real GDP current year – Real GDP previous year) ÷ Real GDP previous year] × 100
GDP per capita = Real GDP ÷ Population
Economic growth is typically measured by the annual percentage change in real GDP, which adjusts for inflation. GDP per capita divides national output by the population, giving a rough measure of living standards. Sustained growth depends on increases in the quantity and quality of factors of production.
经济增长通常以实际 GDP 的年百分比变化来衡量，这一指标已剔除通胀影响。人均 GDP 是将全国产出除以人口，提供了生活水平的粗略衡量。持续增长依赖于生产要素数量与质量的提高。
A positive growth rate signals expansion, but if growth is too rapid it can lead to inflationary pressures and environmental costs.
正增长表明经济扩张，但如果增长过快，可能导致通胀压力和环境成本。
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