📚 Year 8 WJEC Economics: Formula & Theorem Quick Reference Guide | 八年级 WJEC 经济：公式定理速查手册
This guide provides a concise reference for essential economic formulas and principles covered in Year 8 WJEC Economics. Use it to quickly revise the core concepts that explain how people, businesses and economies make decisions.
本指南为八年级 WJEC 经济课程中涉及的关键经济公式与定理提供简明参考。你可以用它快速复习那些解释个人、企业和经济体如何做出决策的核心概念。
1. Scarcity: The Universal Economic Problem | 稀缺性：普遍的经济问题
The basic economic problem arises because resources are limited while human wants are unlimited. This forces individuals and societies to make choices about what to produce, how to produce and for whom to produce.
基本经济问题源于资源有限而人类欲望无限。这迫使个人和社会必须就生产什么、如何生产以及为谁生产做出选择。
Scarcity means we cannot have everything we want. Even a billionaire faces scarcity of time – there are only 24 hours in a day.
稀缺性意味着我们无法拥有一切想要的东西。即便是亿万富翁也面临时间的稀缺——每天只有24小时。
All economic systems, whether market or planned, must answer the three fundamental questions of resource allocation.
所有经济体制，无论是市场体制还是计划体制，都必须回答资源配置的三个基本问题。
2. Opportunity Cost: The Next Best Alternative | 机会成本：次优选择
Opportunity cost is the value of the next best alternative that is given up when a choice is made. It is not the total of all alternatives, only the single most valuable option sacrificed.
机会成本是做出某一选择时所放弃的次优选择的价值。它不是所有被放弃选项的总和，而仅仅是价值最高的那一个被牺牲的选项。
Opportunity Cost = Value of the Next Best Alternative Forgone
机会成本 = 被放弃的次优选择的价值
If you spend one hour studying economics instead of playing video games, the opportunity cost is the enjoyment you lose from not gaming.
如果你花一小时学习经济而不是玩电子游戏，机会成本就是你放弃的游戏乐趣。
Governments also face opportunity cost: spending more on healthcare may mean spending less on education. Every decision involves a trade‑off.
政府也面临机会成本：增加医疗支出可能意味着减少教育支出。每一个决策都包含着权衡取舍。
3. Factors of Production and Their Rewards | 生产要素及其报酬
Economists classify resources into four factors of production, each earning a different form of income.
经济学家将资源分为四类生产要素，每种要素获得不同形式的收入。
Land (natural resources) earns rent. Labour (human effort) earns wages. Capital (man‑made tools and machinery) earns interest. Enterprise (the ability to combine the other three factors and take risks) earns profit.
土地（自然资源）获得地租。劳动（人力付出）获得工资。资本（人造工具和机器）获得利息。企业家才能（组合其他三种要素并承担风险的能力）获得利润。
A farmer uses land (soil, water), labour (farm workers), capital (tractors) and enterprise (the farmer's own business decisions) to grow crops.
农民使用土地（土壤、水）、劳动（农场工人）、资本（拖拉机）和企业家才能（农民自身的经营决策）来种植庄稼。
4. The Law of Demand | 需求定律
The law of demand states that, ceteris paribus (all other things being equal), as the price of a good decreases, the quantity demanded increases, and vice versa. There is an inverse relationship between price and quantity demanded.
需求定律指出，在其他条件不变的情况下，商品价格下降，需求量会增加，反之亦然。价格与需求量之间存在反向关系。
P ↑ → Qd ↓ and P ↓ → Qd ↑
价格上升 → 需求量下降；价格下降 → 需求量上升
A demand curve slopes downwards from left to right. This reflects both the substitution effect (consumers switch to cheaper alternatives when price rises) and the income effect (a higher price reduces consumers' real purchasing power).
需求曲线从左向右下倾。这既反映了替代效应（价格上涨时消费者转向更便宜的替代品），也反映了收入效应（较高价格降低消费者的实际购买力）。
5. The Law of Supply | 供给定律
The law of supply states that, ceteris paribus, as the price of a good increases, the quantity supplied increases. There is a direct relationship between price and quantity supplied.
供给定律指出，在其他条件不变的情况下，商品价格上升，供给量增加。价格与供给量之间存在正向关系。
P ↑ → Qs ↑ and P ↓ → Qs ↓
价格上升 → 供给量上升；价格下降 → 供给量下降
Producers are willing to supply more at higher prices because higher prices can cover rising production costs and lead to higher profits. The supply curve slopes upwards from left to right.
生产者在价格更高时愿意供给更多，因为高价能覆盖上升的生产成本并带来更高利润。供给曲线从左向右上倾。
6. Market Equilibrium | 市场均衡
Market equilibrium occurs at the price where quantity demanded equals quantity supplied. At this point there is no excess demand (shortage) or excess supply (surplus).
市场均衡发生在需求量等于供给量的价格水平上。在这一点，没有超额需求（短缺）或超额供给（过剩）。
Equilibrium: Qd = Qs
均衡状态：需求量 = 供给量
If the price is above the equilibrium, a surplus pushes the price down. If the price is below equilibrium, a shortage pushes the price up. This is the price mechanism, often called the 'invisible hand' by Adam Smith.
如果价格高于均衡水平，过剩会推动价格下跌。如果价格低于均衡水平，短缺会推动价格上涨。这就是价格机制，亚当·斯密常将其称为“看不见的手”。
7. Price Elasticity of Demand (PED) | 需求价格弹性
Price elasticity of demand measures how responsive quantity demanded is to a change in price. It helps businesses predict how a price change will affect total revenue.
需求价格弹性衡量需求量对价格变化的反应程度。它帮助企业预测价格变化如何影响总收入。
PED = %ΔQd ÷ %ΔP
需求价格弹性 = 需求量变动百分比 ÷ 价格变动百分比
price rise leads to a smaller percentage fall in quantity demanded, so total revenue increases. If PED = 1, demand is unit elastic.
若 PED > 1，需求富有弹性：小幅降价会引起需求量大幅增长，从而提高总收入。若 PED < 1，需求缺乏弹性：价格上涨导致需求量下降的比例更小，因此总收入增加。若 PED = 1，需求为单位弹性。
8. Total Revenue and Profit | 总收入与利润
Total revenue (TR) is the money a firm receives from selling its goods. Profit is what remains after all costs are subtracted from total revenue.
总收入是一家企业出售商品所获得的货币金额。利润是总收入扣除所有成本后剩下的部分。
Total Revenue = Price × Quantity Sold
总收入 = 价格 × 销售量
Profit = Total Revenue − Total Cost
利润 = 总收入 − 总成本
A business selling 200 sandwiches at £3 each has total revenue of £600. If total costs are £450, profit is £150. Firms aiming to maximise profit produce where the difference between revenue and cost is greatest.
一家企业以每份3英镑的价格出售200份三明治，总收入为600英镑。若总成本为450英镑，利润则为150英镑。追求利润最大化的企业会在收入与成本之差最大处进行生产。
9. Costs of Production: Fixed, Variable and Total Cost | 生产成本：固定成本、可变成本与总成本
In the short run, a firm faces both fixed costs (which do not change with output, such as rent) and variable costs (which change with output, such as raw materials).
在短期内，企业既面临固定成本（不随产量变化的支出，如租金），也面临可变成本（随产量变化的支出，如原材料）。
Total Cost = Total Fixed Cost + Total Variable Cost
总成本 = 总固定成本 + 总可变成本
g total cost by the quantity produced: ATC = TC ÷ Q. It shows the cost per unit of output.
平均总成本由总成本除以产量得到：ATC = TC ÷ Q。它显示每单位产出的成本。
Understanding cost structures helps a business set prices. If price falls below average variable cost, the firm may need to shut down in the short run.
理解成本结构有助于企业定价。如果价格低于平均可变成本，企业在短期内可能需要停产。
10. The Functions of Money and Simple Interest | 货币的职能与单利
Money is not just coins and notes; it performs several key functions that make trade and saving easier in a modern economy.
货币不仅仅是硬币和纸币；它承担着几项关键职能，使现代经济中的贸易和储蓄更加便利。
Money acts as a medium of exchange (avoids barter), a unit of account (allows prices to be compared) and a store of value (allows saving for the future). These three functions are the cornerstone of any monetary system.
货币充当交换媒介（避免物物交换）、记账单位（便于比较价格）和价值储藏手段（便于为未来储蓄）。这三大职能是任何货币体系的基石。
When money is saved in a bank, it may earn interest. Simple interest is calculated only on the original principal.
当钱存入银行时，它可能获得利息。单利仅以初始本金计算。
Simple Interest = Principal × Rate × Time (I = P × r × t)
单利 = 本金 × 利率 × 时间
Published by TutorHao | Economics Revision Series | aleveler.com
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