Year 9 OCR Economics: Formula & Theorem Quick Reference Handbook | 9年级OCR经济学：公式定理速查手册

📚 Year 9 OCR Economics: Formula & Theorem Quick Reference Handbook | 9年级OCR经济学：公式定理速查手册

Welcome to your go-to quick reference for the essential formulas and theorems in the Year 9 OCR Economics course. This handbook distils the key quantitative and conceptual tools you need to analyse markets, make decisions and understand economic behaviour. Keep it handy for classwork, homework and revision — mastering these building blocks will help you think like an economist.

欢迎使用这本9年级OCR经济学课程必备公式定理速查手册。本手册提炼了你分析市场、做出决策和理解经济行为所需的关键定量与概念工具。课堂练习、家庭作业和考前复习时都可以随时查阅——掌握这些基础模块将帮助你像经济学家一样思考。

1. The Law of Demand | 需求定律

The law of demand states that, ceteris paribus, as the price of a good increases, the quantity demanded decreases, and vice versa. This inverse relationship creates a downward-sloping demand curve. The demand function can be expressed as Qd = a – bP, where ‘a’ is the intercept (quantity demanded when price is zero), ‘b’ is the slope coefficient showing responsiveness, Qd is quantity demanded and P is price.

需求定律指出，在其他条件不变的情况下，商品价格上升时，需求量下降；价格下降时，需求量上升。这种反向关系形成了一条向下倾斜的需求曲线。需求函数可表示为 Qd = a – bP，其中 ‘a’ 是截距（价格为零时的需求量），’b’ 是反映反应程度的斜率系数，Qd 为需求量，P 为价格。

2. The Law of Supply | 供给定律

The law of supply says that, ceteris paribus, as the price of a good rises, the quantity supplied increases. Producers are more willing to supply goods at higher prices because they can earn higher profits. The supply function is often written as Qs = c + dP, where ‘c’ is the intercept (often zero or negative, indicating minimum price needed to supply any quantity), and ‘d’ is the slope showing how responsive supply is to price changes.

供给定律指出，在其他条件不变的情况下，商品价格上升时，供给量增加。生产者在价格更高时更愿意供应商品，因为他们能获得更高的利润。供给函数通常写作 Qs = c + dP，其中 ‘c’ 是截距（常为零或负值，表示开始供给任何数量所需的最低价格），’d’ 是反映供给对价格变化反应程度的斜率。

3. Market Equilibrium | 市场均衡

Market equilibrium occurs where quantity demanded equals quantity supplied (Qd = Qs). At this point, the market clears — there is no surplus or shortage. The equilibrium price (Pe) and equilibrium quantity (Qe) can be found by solving the demand and supply equations simultaneously. Graphically, it is the intersection of the demand and supply curves.

市场均衡出现在需求量等于供给量时（Qd = Qs）。在这个点上，市场出清——没有剩余也没有短缺。均衡价格（Pe）和均衡数量（Qe）可以通过联立求解需求方程和供给方程得出。图形上，它是需求曲线与供给曲线的交点。

4. Price Elasticity of Demand (PED) | 需求的价格弹性

PED measures the responsiveness of quantity demanded to a change in price. The formula is: PED = (% change in quantity demanded) ÷ (% change in price). If |PED| > 1, demand is elastic (sensitive to price); if |PED| < 1, it is inelastic; if |PED| = 1, it is unit elastic. PED is typically negative due to the law of demand, but we often use the absolute value.

PED 衡量需求量对价格变化的反应程度。公式为：PED = （需求量变动的百分比）÷ （价格变动的百分比）。如果 |PED| > 1，需求富有弹性（对价格敏感）；如果 |PED| < 1，需求缺乏弹性；如果 |PED| = 1，则为单位弹性。由于需求定律，PED 通常为负值，但我们常使用其绝对值。

5. Price Elasticity of Supply (PES) | 供给的价格弹性

PES measures how responsive quantity supplied is to a change in price. The formula is: PES = (% change in quantity supplied) ÷ (% change in price). When PES > 1, supply is elastic; when PES < 1, supply is inelastic; when PES = 1, it is unit elastic. Key factors affecting PES include production time, availability of resources, and the ability to store output.

PES 衡量供给量对价格变动的反应程度。公式为：PES = （供给量变动的百分比）÷ （价格变动的百分比）。当 PES > 1 时，供给富有弹性；当 PES < 1 时，供给缺乏弹性；当 PES = 1 时，为单位弹性。影响 PES 的关键因素包括生产时间、资源的可用性以及产出的储存能力。

6. Income Elasticity of Demand (YED) and Cross Elasticity of Demand (XED) | 需求的收入弹性和交叉弹性

YED = (% change in quantity demanded) ÷ (% change in income). This tells us whether a good is a normal good (YED > 0) or an inferior good (YED < 0). XED = (% change in quantity demanded of good A) ÷ (% change in price of good B). XED is positive for substitutes and negative for complements. These elasticities help businesses predict how demand shifts with income changes or competitors' pricing.

YED = （需求量变动的百分比）÷ （收入变动的百分比）。这告诉我们一种商品是正常品（YED > 0）还是低档品（YED < 0）。XED = （商品 A 需求量变动的百分比）÷ （商品 B 价格变动的百分比）。XED 对替代品为正，对互补品为负。这些弹性有助于企业预测需求如何随收入变化或竞争对手定价而变动。

7. Costs of Production: Total, Average and Marginal Cost | 生产成本：总成本、平均成本和边际成本

Total cost (TC) = Fixed cost (FC) + Variable cost (VC). Average total cost (ATC) = TC ÷ Quantity (Q). Marginal cost (MC) = Change in TC ÷ Change in Q. The MC curve eventually rises due to diminishing marginal returns. Understanding costs is vital for pricing and output decisions.

总成本（TC）= 固定成本（FC）+ 可变成本（VC）。平均总成本（ATC）= 总成本 ÷ 数量（Q）。边际成本（MC）= 总成本变化量 ÷ 数量变化量。由于边际收益递减，边际成本曲线最终会上升。理解成本对定价和产量决策至关重要。

8. Revenue and Profit Maximisation | 收益与利润最大化

Total revenue (TR) = Price (P) × Quantity sold (Q). Profit (π) = TR – TC. A firm maximises profit where marginal revenue (MR) equals marginal cost (MC). If MR > MC, the firm should increase output; if MR < MC, it should reduce output. In perfect competition, price equals MR, so the rule becomes P = MC for profit maximisation.

总收益（TR）= 价格（P）× 销售量（Q）。利润（π）= 总收益 – 总成本。当边际收益（MR）等于边际成本（MC）时，企业实现利润最大化。如果 MR > MC，企业应增加产量；如果 MR < MC，则应减少产量。在完全竞争中，价格等于边际收益，因此利润最大化规则变为 P = MC。

9. Opportunity Cost and the Production Possibility Frontier (PPF) | 机会成本与生产可能性边界

Opportunity cost is the value of the next best alternative forgone when a choice is made. The PPF shows the maximum combinations of two goods an economy can produce with given resources. Moving along the PPF involves an opportunity cost. The slope of the PPF, the marginal rate of transformation (MRT), equals the opportunity cost of one good in terms of the other.

机会成本是做出某种选择时所放弃的次优选择的价值。生产可能性边界（PPF）显示了一个经济体在给定资源下能够生产的两种商品的最大组合。沿着 PPF 移动涉及机会成本。PPF 的斜率，即边际转换率（MRT），等于一种商品相对于另一种商品的机会成本。

10. Externalities and Market Failure | 外部性与市场失灵

An externality is a cost or benefit that affects a third party outside the market transaction. Negative externalities (e.g. pollution) lead to overproduction, while positive externalities (e.g. education) lead to underproduction. The formula for social cost is: Social cost = Private cost + External cost. Social benefit = Private benefit + External benefit. Market failure occurs when the free market fails to allocate resources efficiently, often due to externalities, public goods, or imperfect information.

外部性是指影响市场交易之外的第三方的成本或收益。负外部性（如污染）导致过度生产，而正外部性（如教育）导致生产不足。社会成本的公式为：社会成本 = 私人成本 + 外部成本。社会效益 = 私人效益 + 外部效益。当自由市场因外部性、公共物品或信息不完全而无法有效配置资源时，就发生市场失灵。

11. Basic Macroeconomic Indicators | 基本宏观经济指标

Gross Domestic Product (GDP) measures the total value of all final goods and services produced in a country over a period. The expenditure method: GDP = C + I + G + (X – M), where C = consumption, I = investment, G = government spending, X = exports, M = imports. The inflation rate is the percentage change in a price index (e.g. Consumer Price Index) over time. The unemployment rate = (Number of unemployed ÷ Labour force) × 100. These formulas help us track economic performance.

国内生产总值（GDP）衡量一国在一段时期内生产的所有最终商品和服务的总价值。支出法公式为：GDP = C + I + G + (X – M)，其中 C 为消费，I 为投资，G 为政府支出，X 为出口，M 为进口。通货膨胀率是价格指数（如消费者物价指数）随时间变化的百分比。失业率 = （失业人数 ÷ 劳动力人数）× 100。这些公式帮助我们追踪经济表现。

12. The Multiplier Effect and Fiscal Policy | 乘数效应与财政政策

The multiplier effect shows how an initial injection into the economy can lead to a larger final increase in national income. The simple multiplier formula is: k = 1 ÷ (1 – MPC) or k = 1 ÷ MPS, where MPC is the marginal propensity to consume and MPS is the marginal propensity to save (MPC + MPS = 1). Governments use fiscal policy — changes in spending and taxation — to influence aggregate demand. The new equilibrium income can be calculated as ΔY = k × ΔJ, where ΔJ is the initial change in injections.

乘数效应显示，最初注入经济的资金能导致国民收入最终更大的增长。简单乘数公式为：k = 1 ÷ (1 – MPC) 或 k = 1 ÷ MPS，其中 MPC 是边际消费倾向，MPS 是边际储蓄倾向（MPC + MPS = 1）。政府运用财政政策——改变支出和税收——来影响总需求。新的均衡收入可计算为 ΔY = k × ΔJ，其中 ΔJ 是注入的初始变动量。

Published by TutorHao | Economics Revision Series | aleveler.com

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