📚 Year 13 CCEA Economics: Formula & Theorem Quick Reference Handbook | CCEA 经济：公式定理速查手册
This quick reference handbook brings together the essential formulas, definitions and key theorems required for Year 13 CCEA Economics. It is designed to support your revision by presenting each concept clearly and concisely, with worked-style explanations and direct application to the CCEA specification. Use it alongside your class notes and past papers to reinforce your understanding and sharpen your exam technique.
本速查手册汇集了 CCEA Year 13 经济学所要求的关键公式、定义和核心定理，旨在以清晰简明的呈现代每个概念，并结合考试要求提供应用解释，助力你的复习。请将它与课堂笔记和历年真题配合使用，以加深理解并提升应试技巧。
1. Price Elasticity of Demand (PED) | 需求价格弹性
Price elasticity of demand measures the responsiveness of the quantity demanded of a good to a change in its own price.
需求价格弹性衡量一种商品的需求量对其自身价格变化的反应程度。
The basic midpoint formula (to avoid different results depending on direction of change) is shown below.
基本的弧弹性（中点）公式如下，以避免因变化方向不同而得出不同结果。
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。
Demand is price elastic when |PED| e leads to a larger percentage change in quantity demanded. Demand is price inelastic when |PED| < 1. Unit elastic demand occurs when |PED| = 1.
当 |PED| > 1 时，需求富有价格弹性：价格一定百分比的变动会引起需求量更大百分比的变动。当 |PED| < 1 时，需求缺乏价格弹性。单位弹性出现在 |PED| = 1 时。
The relationship between PED and total revenue is vital. If demand is elastic, a price fall raises total revenue; if demand is inelastic, a price rise raises total revenue.
PED 与总收入的关系至关重要。若需求富有弹性，降价会提高总收入；若需求缺乏弹性，提价会提高总收入。
Key determinants of PED include the number and closeness of substitutes, whether the good is a necessity or luxury, the proportion of income spent on the good, and the time period under consideration.
决定 PED 的关键因素包括替代品的数量和相似程度、商品属于必需品还是奢侈品、该商品支出占收入的比例，以及所考虑的时间跨度。
2. Income Elasticity of Demand (YED) | 需求收入弹性
Income elasticity of demand measures the responsiveness of quantity demanded to a change in consumers' income.
需求收入弹性衡量需求量对消费者收入变化的反应程度。
YED = %ΔQd / %ΔY
Normal goods have a positive YED (YED > 0). Luxury goods typically have YED > 1, while necessities have a YED between 0 and 1.
正常品的收入弹性为正（YED > 0）。奢侈品通常 YED > 1，而必需品的 YED 介于 0 与 1 之间。
Inferior goods have a negative YED (YED < 0): as income rises, demand falls.
劣质品的收入弹性为负（YED < 0）：当收入上升时，其需求反而下降。
Firms use YED estimates for forecasting and production planning. During a recession, producers of inferior goods may actually see demand increase.
企业利用 YED 估算进行预测和生产规划。在经济衰退期，劣质品的生产者可能会看到需求上升。
3. Cross Elasticity of Demand (XED) | 需求交叉弹性
Cross elasticity of demand measures the responsiveness of the demand for one good (A) to a change in the price of another good (B).
需求交叉弹性衡量一种商品（A）的需求量对另一种商品（B）价格变化的反应程度。
XED = %ΔQd of A / %ΔP of B
If XED > 0, the two goods are substitutes (e.g. tea and coffee). If XED < 0, they are complements (e.g. printers and ink cartridges). An XED close to zero suggests the goods are unrelated.
若 XED > 0，两种商品互为替代品（如茶与咖啡）。若 XED < 0，则互为互补品（如打印机与墨盒）。XED 接近于零说明两者是无关商品。
Firms track XED to assess the impact of rivals' pricing strategies and to design promotional bundles for complementary products.
企业追踪 XED 以评估竞争对手定价策略的影响，并为互补品设计促销组合。
4. Price Elasticity of Supply (PES) | 供给价格弹性
Price elasticity of supply measures the responsiveness of quantity supplied to a change in the price of the good.
供给价格弹性衡量供给量对商品自身价格变化的反应程度。
PES = %ΔQs / %ΔP
1. Perfectly inelastic supply gives PES = 0; perfectly elastic supply is shown as PES → ∞.
当 PES > 1 时供给富有弹性，PES < 1 时供给缺乏弹性，PES = 1 时为单位弹性。完全无弹性供给的 PES = 0，完全弹性供给的 PES 趋近于无穷大。
Determinants of PES include the length of the production period, spare capacity, the ease of storing stocks, and the mobility of factors of production. Supply tends to become more elastic over longer time horizons.
决定 PES 的因素包括生产周期的长短、闲置产能、库存的便利程度以及生产要素的流动性。时间跨度越长，供给通常变得越有弹性。
5. Costs, Revenue and Profit | 成本、收益与利润
A firm' ost (TVC): TC = TFC + TVC. Average cost (AC) is total cost divided by output: AC = TC / Q.
企业的总成本 (TC) 为总固定成本 (TFC) 与总可变成本 (TVC) 之和：TC = TFC + TVC。平均成本 (AC) 是总成本除以产量：AC = TC / Q。
Marginal cost (MC) measures the change in total cost when one more unit is produced.
边际成本 (MC) 衡量多生产一单位产品所引起的总成本变化。
MC = ΔTC / ΔQ
al revenue (MR) is the change in total revenue from selling one extra unit: MR = ΔTR / ΔQ.
总收益 (TR) 是价格乘以销售量：TR = P × Q。平均收益 (AR) 是总收益除以销售量，等于价格：AR = TR / Q = P。边际收益 (MR) 是多销售一单位产品所带来的总收益变化：MR = ΔTR / ΔQ。
Profit is the difference between total revenue and total cost: Profit = TR – ormal profit is included in total cost; supernormal (abnormal) profit occurs when TR > TC.
利润是总收益与总成本之间的差额：利润 = TR – TC。正常利润已包含在总成本中；当 TR > TC 时，出现超常（超额）利润。
6. Profit Maximisation Rule | 利润最大化法则
The profit-maximising level of output occurs where marginal cost equals marginal revenue, provided that MC cuts MR from below.
当边际成本等于边际收益且 MC 从下方穿过 MR 时，产量达到利润最大化水平。
Profit maximisation: MC = MR
If MC < MR, the firm can increase profit by expanding output. If MC > MR, the firm should reduce output.
若 MC < MR，企业可通过扩大产量增加利润；若 MC > MR，则应当缩减产量。
This rule applies to all market structures – perfect competition, monopolistic competition, oligopoly and monopoly – although the shape of MR differs.
这一法则适用于所有市场结构——完全竞争、垄断竞争、寡头和垄断——尽管 MR 的形状有所不同。
= AR = price, so the rule becomes P = MC at the profit-maximising output in the short run.
在完全竞争市场中，MR = AR = 价格，因此该法则表现为短期利润最大化产量处 P = MC。
7. The Multiplier Effect | 乘数效应
The multiplier (k) measures the magnified impact of an initial injection into the circular flow of income on the final level of national income.
乘数 (k) 衡量初始注入到收入循环流量中的金额对最终国民收入水平的放大效应。
ΔNational Income = k × ΔInjection
s on The simple multiplier depends on the marginal propensity to consume (MPC) and the marginal propensity to save (MPS = 1 – MPC).
简单乘数取决于边际消费倾向 (MPC) 和边际储蓄倾向 (MPS = 1 – MPC)。
k = 1 / (1 – MPC) = 1 / MPS
In a more realistic open economy with government, additional withdrawals arise: the marginal propensity to tax (MPT) and the marginal propensity to import (MPM). The multiplier becomes smaller.
在一个包含政府部门的现实开放经济中，还会产生额外的漏出：边际税收倾向 (MPT) 和边际进口倾向 (MPM)，此时乘数会变小。
k = 1 / (MPS + MPT + MPM)
A higher MPC leads to a larger multiplier; higher rates of saving, taxation or spending on imports reduce the multiplier.
MPC 越高，乘数越大；较高的储蓄率、税率或进口支出会减小乘数。
8. Aggregate Demand (AD) | 总需求
Aggregate demand is the total planned expenditure on goods and services produced within an economy over a given period.
总需求是在一定时期内，对一个经济体内所生产的商品和服务的计划支出总额。
AD = C + I + G + (X – M)
C is household consumption expenditure, I is investment spending by firms, G is government spending on goods and services, X is exports, and M is imports.
C 为家庭消费支出，I 为企业投资支出，G 为政府对商品和服务的支出，X 为出口，M 为进口。
The AD curve slopes downwards, reflecting the wealth effect, the interest‑rate effect and the international trade effect.
总需求曲线向下倾斜，反映了财富效应、利率效应和国际贸易效应。
Changes in any component shift the AD curve, influencing real GDP and the price level. Expansionary fiscal or monetary policy aims to boost AD.
任一组分的变化都会引起 AD 曲线移动，进而影响实际 GDP 和价格水平。扩张性财政或货币政策旨在提高总需求。
9. Quantity Theory of Money | 货币数量论
The quantity theory of money is expressed through the Fisher equation of exchange.
货币数量论由费雪交易方程式表达。
MV = PT
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