Year 10 WJEC Economics: Key Formulas & Theorems Quick Reference | 10年级 WJEC 经济：核心公式定理速查手册

📚 Year 10 WJEC Economics: Key Formulas & Theorems Quick Reference | 10年级 WJEC 经济：核心公式定理速查手册

This revision note provides a concise compilation of essential formulas and economic theorems covered in the Year 10 WJEC Economics syllabus. Designed for quick reference and bilingual learning, each section pairs clear English explanations with precise Chinese translations. Whether you are reviewing demand elasticities, cost calculations, or macroeconomic indicators, this handbook gives you the tools to score top marks.

这篇速查笔记汇集了 WJEC 十年级经济学课程中的核心公式与定理，专为快速检索与双语学习设计。每个小节均将清晰的英文阐释与准确的中文翻译配对呈现。无论你是在复习需求弹性、成本计算还是宏观经济指标，本手册都能为你提供夺取高分的利刃。

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1. Demand, Supply and Market Equilibrium | 需求、供给与市场均衡

The law of demand states that, ceteris paribus, as the price of a good rises, the quantity demanded falls. This inverse relationship gives the demand curve its downward slope. A linear demand function is often expressed as:

需求定律指出，在其他条件不变的情况下，价格上升，需求量下降。这种反向关系使需求曲线向下倾斜。线性需求函数通常表示为：

Qd = a – bP

where Qd is quantity demanded, P is price, a is the intercept (quantity demanded when price is zero), and b is the slope (change in Qd per unit change in price).

其中 Qd 为需求量，P 为价格，a 表示截距（价格为零时的需求量），b 表示斜率（价格每变动一单位所引起的需求量变动）。

The law of supply shows a positive relationship: as price increases, quantity supplied increases. A simple linear supply function is:

供给定律呈正相关关系：价格上升，供给量上升。一个简单的线性供给函数为：

Qs = c + dP

where Qs is quantity supplied, c is the minimum quantity supplied when price is zero, and d shows the responsiveness of supply to price changes.

其中 Qs 为供给量，c 为价格为零时的基础供给量，d 反映供给对价格变化的反应程度。

Market equilibrium occurs where demand equals supply: Qd = Qs. Setting a – bP = c + dP and solving for P gives the equilibrium price:

市场均衡发生在需求等于供给之处：Qd = Qs。令 a – bP = c + dP 并对 P 求解，得到均衡价格：

P* = (a – c) / (b + d)

Substituting P* back into either function gives the equilibrium quantity Q*.

将 P* 代回任一函数即得均衡数量 Q*。

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2. 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 basic formula is:

需求价格弹性衡量需求量对价格变动的反应程度。基本公式为：

PED = % change in Qd ÷ % change in P

Using the midpoint (arc) method for more accuracy across a range:

使用中点法（弧弹性）在区间的计算更准确：

PED = [(Q₂ – Q₁) / ((Q₂ + Q₁)/2)] ÷ [(P₂ – P₁) / ((P₂ + P₁)/2)]

Key interpretations are summarised below:

主要解读归纳如下：

PED value (English)	中文含义
|PED| > 1: Elastic	弹性｜Ed｜>1：富有弹性
|PED| = 1: Unit elastic	｜Ed｜=1：单位弹性
|PED| < 1: Inelastic	｜Ed｜<1：缺乏弹性
|PED| = 0: Perfectly inelastic	｜Ed｜=0：完全无弹性
|PED| → ∞: Perfectly elastic	｜Ed｜→∞：完全弹性

revenue; if inelastic, a price rise increases total revenue. Total revenue is TR = P × Q.

总收入检验是一项实用定理：如果需求富有弹性，提价会减少总收入；如果缺乏弹性，提价会增加总收入。总收入 TR = P × Q。

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3. Price Elasticity of Supply (PES) | 供给价格弹性

PES quantifies how much the quantity supplied changes when price changes. The formula mirrors PED:

供给价格弹性量化了当价格变化时供给量的变动程度。其公式与 PED 相似：

PES = % change in Qs ÷ % change in P

Using the midpoint method if required:

必要时使用中点法：

PES = [(Q₂ – Q₁) / ((Q₂ + Q₁)/2)] ÷ [(P₂ – P₁) / ((P₂ + P₁)/2)]

PES values greater than 1 indicate elastic supply (producers can adjust output easily); less than 1 indicates inelastic supply. Determinants include time period, spare capacity, and complexity of production.

PES 大于 1 表示供给弹性充足（生产者较易调整产量）；小于 1 表示供给缺乏弹性。决定因素包括时间周期、闲置产能与生产复杂程度。

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4. Income Elasticity of Demand (YED) & Cross Elasticity of Demand (XED) | 收入弹性与交叉弹性

Income elasticity of demand links quantity demanded to changes in consumer income:

收入弹性将需求量与消费者收入的变化联系起来：

YED = % change in Qd ÷ % change in income (Y)

A positive YED signals a normal good (luxury if YED > 1, necessity if 0 < YED < 1). A negative YED indicates an inferior good.

YED 为正代表正常品（若大于 1 为奢侈品，介于 0 至 1 之间为必需品）；YED 为负则代表劣等品。

Cross elasticity of demand measures how the quantity demanded of one good (A) responds to a price change of another good (B):

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：

XED = % change in Qd of A ÷ % change in price of B

Positive XED means A and B are substitutes; negative XED means they are complements. Near-zero XED suggests independent goods.

XED 为正表明 A 与 B 互为替代品；XED 为负表明二者为互补品；接近于零则说明商品相互独立。

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5. Costs of Production | 生产成本

Understanding cost structures is vital for supply decisions. Total cost (TC) is the sum of total fixed cost (TFC) and total variable cost (TVC):

理解成本结构对供给决策至关重要。总成本（TC）等于总固定成本（TFC）与总可变成本（TVC）之和：

TC = TFC + TVC

Average (unit) costs are derived as follows:

平均（单位）成本由以下公式得出：

ATC (or AC) = TC / Q

AFC = TFC / Q

AVC = TVC / Q

Marginal cost is the extra cost of producing one more unit:

边际成本是额外生产一个单位所带来的附加成本：

MC = ΔTC / ΔQ

The shape of cost curves obeys the law of diminishing returns: initially MC falls as specialisation increases, but eventually MC rises. The MC curve always passes through the minimum points of the AVC and ATC curves.

成本曲线的形状遵循边际报酬递减规律：起初因专业化使边际成本下降，但最终边际成本上升。MC 曲线总是穿过 AVC 曲线与 ATC 曲线的最低点。

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6. Revenue, Profit and Profit Maximisation | 收入、利润与利润最大化

Total revenue, average revenue and marginal revenue are fundamental to a firm's decision-making:

总收入、平均收入与边际收入是厂商决策的基础：

TR = P × Q

AR = TR / Q (= P, for a uniform price)

MR = ΔTR / ΔQ

Profit (π) is the difference between total revenue and total cost:

利润（π）为总收入与总成本之差：

π = TR – TC

hat MR > MC before that point and MR < MC afterwards. This holds in all market structures.

利润最大化的原则是，厂商应将产量定在边际收入等于边际成本（MR = MC）的水平，前提是在此前 MR > MC，在此后 MR < MC。这一规律适用于所有市场结构。

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7. Market Structures | 市场结构

emand curve facing the firm is horizontal. The profit-maximising condition becomes P = MC.

收益曲线的形态取决于市场结构。在完全竞争下，厂商是价格接受者，故 AR = MR = P，其面临的需求曲线是水平的。利润最大化条件即 P = MC。

ation, the monopolist produces where MR = MC and then charges a price read from the demand curve (above MC).

在垄断市场中，企业是整个行业的需求者，价格由其自行制定，需求曲线向右下方倾斜。MR 位于 AR 之下，为实现利润最大化，垄断者按 MR = MC 确定产量，再依据需求曲线收取高于 MC 的价格。

Other structures like oligopoly and monopolistic competition have intermediate features; key theorems include interdependence and differentiated products.

寡头垄断与垄断竞争等结构兼具二者特征，重点定理包括相互依赖性与产品差异化。

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8. Macroeconomic Indicators and the Multiplier | 宏观经济指标与乘数

Gross Domestic Product (GDP) by the expenditure approach is calculated as:

支出法核算的国内生产总值（GDP）计算公式为：

GDP = C + I + G + (X – M)

where C is consumption, I investment, G government spending, X exports and M imports.

其中 C 为消费，I 为投资，G 为政府支出，X 为出口，M 为进口。

The inflation rate (using a price index) measures the percentage increase in the general price level:

通货膨胀率（通过价格指数计算）衡量总体物价水平的上升百分比：

Inflation rate = [(CPIₙₑₓ – CPIₒₗₔ) / CPIₒₗₔ] × 100%

The unemployment rate reflects the proportion of the labour force actively seeking work:

失业率反映了积极寻找工作的劳动力占比：

Unemployment rate = (Number unemployed / Labour force) × 100%

The multiplier effect explains how an initial injection of spending leads to a larger final increase in national income. The simple multiplier (k) is:

乘数效应解释了一笔初始支出注入如何带来国民收入更大幅度的最终增长。简单乘数（k）为：

k = 1 / (1 – MPC) = 1 / MPS

omprehensive formula may be used, but the core principle remains: ΔY = k × ΔJ (injection).

其中 MPC 为边际消费倾向，MPS 为边际储蓄倾向（MPC + MPS = 1）。若将税收与进口纳入考量，可使用更复杂的公式，但核心原理不变：ΔY = k × ΔJ（注入量）。

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Published by TutorHao | Economics Revision Series | aleveler.com

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