📚 IGCSE AQA Economics: Formula Handbook | IGCSE AQA 经济：公式汇总手册
This handbook compiles all the essential formulas you need for the IGCSE AQA Economics examination. From percentage changes to elasticity, costs, revenues, and macroeconomic indicators, mastering these calculations is crucial for AO2 marks. Each formula is explained with clear definitions and a step-by-step breakdown to help you apply them confidently in exam questions.
本手册汇总了 IGCSE AQA 经济学考试所需的所有关键公式。从百分比变化到弹性、成本、收入和宏观经济指标，掌握这些计算对于获得 AO2 分数至关重要。每个公式都附带清晰的定义和分步解释，帮助你在考试中自信应用。
1. Percentage Change | 百分比变化
Percentage change is the foundation of many economic calculations, including elasticity. It measures how much a variable has increased or decreased relative to its original value. The general formula is:
百分比变化是许多经济学计算的基础，包括弹性。它衡量一个变量相对于其原始值增加或减少了多少。通用公式为：
% Change = (New Value – Original Value) / Original Value × 100
For example, if the price of a good rises from £20 to £25, the percentage change in price is ((25 – 20) ÷ 20) × 100 = 25%. Always remember to state whether the change is an increase (+) or decrease (-) when interpreting elasticity.
例如，如果一种商品的价格从 20 英镑上升到 25 英镑，价格变动的百分比为 ((25 – 20) ÷ 20) × 100 = 25%。在解释弹性时，请务必说明变动是增加 (+) 还是减少 (-)。
2. Price Elasticity of Demand (PED) | 需求价格弹性
PED measures the responsiveness of quantity demanded to a change in price. It is always negative (law of demand), but we often ignore the minus sign and consider its absolute value. PED is calculated as:
PED 衡量需求量对价格变动的反应程度。它总是负值（需求定律），但我们通常忽略负号，考虑其绝对值。PED 计算公式为：
PED = % change in quantity demanded / % change in price
Interpretation: |PED| > 1 => elastic demand (luxuries, substitutes available). |PED| < 1 => inelastic demand (necessities, addictive goods). |PED| = 1 => unit elastic. A firm’s total revenue increases when price rises if demand is inelastic, and decreases if demand is elastic.
解读：|PED| > 1 => 富有弹性（奢侈品、有替代品）。|PED| < 1 => 缺乏弹性（必需品、成瘾品）。|PED| = 1 => 单位弹性。如果需求缺乏弹性，价格上升会使企业总收入增加；如果需求富有弹性，价格上升则会使总收入减少。
3. Price Elasticity of Supply (PES) | 供给价格弹性
PES measures how responsive quantity supplied is to a change in price. It is normally positive because supply curves slope upward. The formula is:
PES 衡量供给量对价格变动的反应程度。通常为正值，因为供给曲线向上倾斜。公式为：
PES = % change in quantity supplied / % change in price
Key factors include time period (more elastic in the long run), spare capacity, and ease of factor substitution. PES > 1 => elastic supply (firms can increase output easily). PES < 1 => inelastic supply (limited ability to raise output).
关键因素包括时间周期（长期更富有弹性）、闲置产能和要素替代的难易程度。PES > 1 => 供给弹性充足（企业可轻松增产）。PES < 1 => 供给缺乏弹性（增产能力有限）。
4. Income Elasticity of Demand (YED) | 需求收入弹性
YED measures the responsiveness of demand to changes in consumer income. It indicates whether a good is normal or inferior. Formula:
YED 衡量需求对消费者收入变动的反应程度。它表明商品是正常品还是劣等品。公式为：
YED = % change in quantity demanded / % change in income
If YED > 0 (positive), the good is a normal good (demand rises with income). If YED > 1, it is a luxury good. If 0 < YED < 1, it is a necessity. If YED < 0 (negative), the good is inferior (demand falls as income rises).
如果 YED > 0（正值），该商品为正常品（需求随收入增加而上升）。若 YED > 1，则为奢侈品。若 0 < YED < 1，则为必需品。若 YED < 0（负值），则为劣等品（收入增加时需求下降）。
5. Cross Elasticity of Demand (XED) | 需求交叉弹性
XED measures how the demand for one good responds to a price change of another good. It determines whether goods are substitutes or complements. Formula:
XED 衡量一种商品的需求对另一种商品价格变动的反应程度。它决定商品是替代品还是互补品。公式为：
XED = % change in quantity demanded of good A / % change in price of good B
If XED > 0 (positive), the two goods are substitutes (e.g., tea and coffee). If XED < 0 (negative), they are complements (e.g., printers and ink). The larger the absolute value, the closer the relationship. XED near 0 suggests unrelated goods.
如果 XED > 0（正值），两种商品互为替代品（如茶和咖啡）。如果 XED < 0（负值），则互为互补品（如打印机和墨盒）。绝对值越大，关系越紧密。XED 接近 0 表明商品不相关。
6. Costs of Production | 生产成本
Understanding costs is vital for analysis of firm behaviour. Here are the core cost formulas:
理解成本对于分析企业行为至关重要。以下是核心成本公式：
Total Cost (TC) = Total Fixed Cost (TFC) + Total Variable Cost (TVC)
Fixed costs do not vary with output (e.g., rent), while variable costs change with output (e.g., raw materials). Average cost shows the cost per unit of output:
固定成本不随产量变化（如租金），而可变成本随产量变化（如原材料）。平均成本表示每单位产出的成本：
Average Cost (AC or ATC) = TC / Quantity (Q)
Average Fixed Cost (AFC) = TFC / Q; Average Variable Cost (AVC) = TVC / Q. Marginal cost (MC) is the cost of producing one extra unit:
平均固定成本 (AFC) = TFC / Q；平均可变成本 (AVC) = TVC / Q。边际成本 (MC) 是额外生产一单位产品所增加的成本：
MC = Change in TC / Change in Q
Remember, as output increases, AFC falls continuously, while AVC and MC tend to fall then rise due to the law of diminishing returns.
请记住，随着产量增加，AFC 持续下降，而 AVC 和 MC 会因边际报酬递减规律先降后升。
7. Revenue and Profit | 收入与利润Published by TutorHao | IGCSE Economics Revision Series | aleveler.com
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