📚 Year 10 OCR Economics Formulae & Key Theorems Quick Reference Guide | Year 10 OCR 经济：公式定理速查手册
This compact revision guide brings together the essential formulae, ratios and key economic relationships you need to master for the OCR GCSE Economics (9-1) course. Understanding how to calculate and interpret each one will strengthen your analysis for both multiple-choice questions and longer written answers. Keep it handy for quick self-testing.
这份精简的速查手册汇总了 OCR GCSE 经济 (9-1) 课程中必须掌握的核心公式、比率和关键经济关系。理解如何计算和解读每一项，能帮助你在选择题和长篇写作题中提升分析质量。请随时使用它进行快速自测。
1. Calculating Percentage Changes | 百分比变化计算
Percentage change is the most frequently used calculation in economics. It allows you to compare the size of a change relative to the starting value, which is vital for measuring elasticities, growth and inflation.
百分比变化是经济学中最常用的计算工具，它让你能够比较变化相对于起始值的大小，这对于衡量弹性、增长和通货膨胀至关重要。
% Change = (New Value − Original Value) ÷ Original Value × 100
If the original price is £25 and it rises to £30, the percentage increase is: (30 − 25) ÷ 25 × 100 = 20%. A fall from 200 to 180 gives a change of −10%.
如果原价是25英镑，上涨到30英镑，涨幅为 (30 − 25) ÷ 25 × 100 = 20%。如果从200下跌到180，百分比变化为 −10%。
2. Price Elasticity of Demand (PED) | 需求价格弹性
PED measures how strongly quantity demanded responds to a change in price. It helps firms predict the impact of pricing decisions on total revenue.
PED 衡量需求量对价格变化的反应强度，能帮助企业预判定价决策对总收益的影响。
PED = %Δ Quantity Demanded ÷ %Δ Price
The sign of PED is almost always negative, but we often ignore the minus sign and focus on the absolute value. The following table summarises the possible outcomes:
PED 的符号通常为负数，但考试中我们常使用绝对值。下表总结了各种可能的情形：
| PED Value | Interpretation |
|---|---|
| PED > 1 | Price elastic (富有弹性) |
| PED < 1 | Price inelastic (缺乏弹性) |
| PED = 1 | Unitary elastic (单位弹性) |
| PED = 0 | Perfectly inelastic (完全无弹性) |
| PED = ∞ | Perfectly elastic (完全弹性) |
When demand is price elastic, cutting price raises total revenue. When demand is price inelastic, raising price raises total revenue. For unitary elastic demand, revenue stays constant.
当需求富有弹性时，降价会增加总收益；当需求缺乏弹性时，提价会增加总收益；单位弹性下总收益保持不变。
3. Price Elasticity of Supply (PES) | 供给价格弹性
PES shows how responsive quantity supplied is to a change in price. It depends on factors such as spare capacity, stock levels and the complexity of the production process.
PES 表示供给量对价格变化的反应程度，它取决于闲置产能、库存水平和生产过程的复杂程度等因素。
PES = %Δ Quantity Supplied ÷ %Δ Price
| PES Value | Interpretation |
|---|---|
| PES > 1 | Price elastic supply (富有弹性) |
| PES < 1 | Price inelastic supply (缺乏弹性) |
| PES = 0 | Perfectly inelastic (完全无弹性) |
| PES = ∞ | Perfectly elastic (完全弹性) |
Supply is usually price elastic in the long run because firms can adjust all factors of production. In the short run, supply tends to be more price inelastic.
在长期，企业可以调整所有生产要素，供给通常富有弹性；在短期，供给往往更缺乏弹性。
4. Income Elasticity of Demand (YED) | 需求收入弹性
YED measures how demand for a product changes in response to a change in consumer incomes. It is key to classifying goods as normal, luxury, necessity or inferior.
YED 衡量产品需求对消费者收入变化的反应程度，是区分正常品、奢侈品、必需品和劣等品的关键指标。
YED = %Δ Quantity Demanded ÷ %Δ Income
| YED Value | Interpretation |
|---|---|
| YED > 1 | Luxury good (奢侈品) |
| 0 < YED < 1 | Necessity (必需品) |
| YED < 0 | Inferior good (劣等品) |
During a recession, demand for inferior goods rises while demand for luxury goods falls. A positive YED indicates a normal good; a negative YED indicates an inferior good.
经济衰退时，劣等品需求上升、奢侈品需求下降。YED 为正表示正常品，YED 为负表示劣等品。
5. Cross-Price Elasticity of Demand (XED) | 需求交叉价格弹性
XED reveals the relationship between two goods by measuring how the demand for Good A reacts to a price change in Good B. It helps firms identify their close substitutes and complements.
XED 通过衡量商品A的需求对商品B价格变化的反应来揭示两种商品的关系，帮助企业识别替代品和互补品。
XED = %Δ Quantity Demanded of Good A ÷ %Δ Price of Good B
| XED Value | Interpretation |
|---|---|
| XED > 0 | Substitutes (替代品) |
| XED < 0 | Complements (互补品) |
| XED ≈ 0 | Unrelated goods (无关商品) |
A high positive XED (e.g. +2.5) means the goods are close substitutes; a significant negative XED (e.g. −1.1) means they are strong complements.
较高的正 XED（例如 +2.5）表示商品是近似的替代品；明显的负 XED（例如 −1.1）表示商品是强互补品。
6. Total Revenue, Total Cost and Profit | 总收益、总成本与利润
A firm's financial performance hinges on the relationships between revenue, cost and profit. These simple equations form the backbone of business decision-making.
企业的财务表现取决于收益、成本和利润之间的关系，这些简单公式是商业决策的基础。
Total Revenue (TR) = Price per unit (P) × Quantity sold (Q)
Total Cost (TC) = Total Fixed Cost (TFC) + Total Variable Cost (TVC)
Profit = TR − TC
Fixed costs do not vary with output (e.g. rent), while variable costs change directly with production (e.g. raw materials). If TR exceeds TC, the firm earns a supernormal profit; if TR is below TC, it makes a loss.
固定成本不随产量变化（如租金），可变成本与产量直接相关（如原材料）。若总收益大于总成本，企业获得超额利润；若总收益低于总成本，企业亏损。
7. Break-even Analysis | 盈亏平衡分析
The break-even point is the level of output where total revenue exactly equals total cost, giving zero profit. It is a vital reference for financial planning and risk assessment.
盈亏平衡点是总收益恰好等于总成本的产量水平，此时利润为零，是财务规划和风险评估的重要参考。
ven Output (units) = Total Fixed Costs ÷ (Selling Price per unit − Variable Cost per unit)
The denominator (Price − Unit Variable
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