📚 Year 11 Eduqas Economics: Quick Revision Guide to Formulas and Principles | Eduqas 经济：公式定理速查手册
This handy reference booklet compiles all the essential formulas, equations, and key economic principles you need to master for the Eduqas GCSE (9-1) Economics examination. Use this guide to quickly revise calculation methods, interpret elasticity values, understand production costs, and recall vital macroeconomic indicators.
本速查手册汇集了Eduqas GCSE（9-1）经济学考试必须掌握的所有核心公式、等式和关键经济原理。利用本指南快速复习计算方法、解读弹性数值、理解生产成本以及记忆重要的宏观经济指标。
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 price. The formula is:
需求价格弹性衡量需求量对价格变动的反应程度。计算公式为：
PED = %ΔQd / %ΔP
where %ΔQd is the percentage change in quantity demanded and %ΔP is the percentage change in price.
其中 %ΔQd 为需求量的百分比变化，%ΔP 为价格的百分比变化。
The numerical value of PED is usually negative due to the law of demand, but the minus sign is often ignored. Interpretations:
根据需求定律，PED 数值通常为负数，但实际中常忽略负号。解读如下：
| PED Value (absolute) | Term | Meaning |
|---|---|---|
| > 1 | Price elastic | %ΔQd > %ΔP; demand is responsive |
| < 1 | Price inelastic | %ΔQd < %ΔP; demand is unresponsive |
| = 1 | Unit elastic | %ΔQd = %ΔP; total revenue stays constant |
| = 0 | Perfectly inelastic | Quantity demanded does not change when price changes |
| = ∞ | Perfectly elastic | Any price increase reduces quantity demanded to zero |
PED determines the effect of a price change on total revenue: if demand is elastic, a price rise will reduce total revenue; if inelastic, a price rise will increase total revenue.
PED 决定价格变化对总收益的影响：如果需求富有弹性，提价会减少总收益；如果缺乏弹性，提价会增加总收益。
2. Income Elasticity of Demand (YED) | 需求收入弹性
Income elasticity of demand shows how quantity demanded changes as consumer income changes. Formula:
需求收入弹性反映消费者收入变化时需求量的变动程度。公式：
YED = %ΔQd / %ΔY
where %ΔY is the percentage change in income.
其中 %ΔY 为收入的百分比变化。
Normal goods have a positive YED (>0). Inferior goods have a negative YED (<0). For luxury goods, YED > +1; for necessities, 0 < YED < 1.
正常品的 YED 为正（>0），低档品的 YED 为负（<0）。奢侈品的 YED > +1，必需品的 YED 介于 0 和 1 之间。
3. Price Elasticity of Supply (PES) | 供给价格弹性
PES measures the responsiveness of quantity supplied to a change in price.
供给价格弹性衡量供给量对价格变动的反应程度。
PES = %ΔQs / %ΔP
Supply can be elastic (>1), inelastic (<1), unit elastic (=1), perfectly inelastic (=0), or perfectly elastic (∞). Factors affecting PES include production time, spare capacity, and ease of storage.
供给弹性可分为富有弹性（>1）、缺乏弹性（<1）、单位弹性（=1）、完全无弹性（=0）和完全弹性（∞）。影响 PES 的因素包括生产周期、闲置产能和储存难易程度。
4. Costs of Production | 生产成本
Total cost (TC) is the sum of total fixed costs (TFC) and total variable costs (TVC).
总成本（TC）是总固定成本（TFC）与总可变成本（TVC）之和。
TC = TFC + TVC
Average total cost (ATC) is the cost per unit of output.
平均总成本（ATC）是每单位产出的成本。
ATC = TC ÷ Q
Marginal cost (MC) is the extra cost of producing one more unit.
边际成本（MC）是多生产一单位产品所增加的成本。
MC = ΔTC ÷ ΔQ
The MC curve usually passes through the minimum points of both the ATC and AVC curves.
边际成本曲线通常穿过平均总成本曲线和平均可变成本曲线的最低点。
5. Revenue and Profit | 收益与利润
Total revenue (TR) is the money a firm receives from sales.
总收益（TR）是企业从销售中获得的收入。
TR = Price × Quantity
Average revenue (AR) equals price and is the revenue per unit sold. AR = TR ÷ Q.
平均收益（AR）等于价格，即每单位销售的收益。AR = TR ÷ Q
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