📚 Year 7 OCR Economics: Formula & Theorem Quick Reference Handbook | 7年级OCR经济：公式定理速查手册
Welcome to your handy quick-reference guide for Year 7 OCR Economics. This handbook brings together the essential formulas, rules, and principles you will meet in the classroom. Use it to revise, test yourself, or look up a definition in seconds. Each section explains one key economic idea, first in English then in Chinese, so you can master the vocabulary and the concepts at the same time.
欢迎使用这本实用的7年级OCR经济速查手册。本手册汇集了你在课堂上会遇到的所有基本公式、法则和原理。你可以用它来复习、自我测试，或者快速查找定义。每个章节首先用英文讲解，再用中文解释同一个核心经济思想，帮助你同时掌握术语和概念。
1. The Basic Economic Problem | 基本经济问题
The basic economic problem arises because our wants are unlimited, but the resources available to satisfy them are scarce. This forces individuals, firms, and governments to make choices about how to allocate resources.
基本经济问题的产生是因为我们的欲望是无限的，而用于满足这些欲望的资源是稀缺的。这迫使个人、企业和政府必须就如何分配资源做出选择。
The concept can be summarised by the triad: Scarcity → Choice → Opportunity Cost. Every decision involves giving up the next best alternative.
这一概念可以用三要素概括：稀缺 → 选择 → 机会成本。每一个决定都意味着放弃了次优替代方案。
- Unlimited wants vs. limited resources | 无限的欲望与有限的资源
- We must choose what to produce, how to produce it, and for whom | 必须选择生产什么、如何生产以及为谁生产
2. Opportunity Cost | 机会成本
Opportunity cost is the value of the next best alternative that you give up when making a choice. It is not just money – it includes time, enjoyment, and other benefits lost.
机会成本是你在做出选择时放弃的次优替代方案的价值。它不仅指金钱——还包括时间、乐趣以及其他失去的好处。
Opportunity Cost = Value of Next Best Alternative Foregone
机会成本 = 所放弃的次优替代方案的价值
For example, if you spend an hour studying economics instead of playing video games, the opportunity cost is the enjoyment and relaxation you would have gained from gaming.
例如，如果你用一个小时学习经济学而不是玩电子游戏，机会成本就是玩电子游戏本可以带来的乐趣和放松。
This principle reminds us that every choice has a cost, even when nothing is paid in cash.
这一原则提醒我们，每一个选择都有代价，即使没有支付任何现金。
3. Law of Demand and Demand Curve | 需求定律与需求曲线
The law of demand states that, all other things being equal, as the price of a good rises, the quantity demanded falls; as the price falls, the quantity demanded rises. This inverse relationship is shown by a downward-sloping demand curve.
需求定律指出，在其他条件不变的情况下，商品价格上升，需求量下降；价格下降，需求量上升。这种反向关系体现为一条向下倾斜的需求曲线。
P ↑ → Qd ↓ | P ↓ → Qd ↑
价格上升 → 需求量减少 | 价格下降 → 需求量增加
The demand curve is drawn with price on the vertical axis and quantity on the horizontal axis. Factors that shift the whole demand curve include changes in income, tastes, the price of related goods, and advertising.
需求曲线以价格为纵轴、数量为横轴。引起整条需求曲线移动的因素包括收入变化、偏好变化、相关商品价格以及广告。
4. Law of Supply and Supply Curve | 供给定律与供给曲线
The law of supply says that, ceteris paribus, as the price of a good rises, the quantity supplied rises; as the price falls, the quantity supplied falls. This positive relationship creates an upward-sloping supply curve.
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；价格下降，供给量减少。这种正相关关系形成了一条向上倾斜的供给曲线。
P ↑ → Qs ↑ | P ↓ → Qs ↓
价格上升 → 供给量增加 | 价格下降 → 供给量减少
Shifts in the supply curve occur when there are changes in production costs, technology, the number of sellers, or government taxes and subsidies. A move along the curve only happens due to a change in the good’s own price.
当生产成本、技术、卖家数量或政府税收与补贴发生变化时，供给曲线会发生移动。只有商品自身价格的变化才会引起沿曲线的移动。
5. Market Equilibrium | 市场均衡
Market equilibrium occurs at the price where the quantity demanded equals the quantity supplied. At this point there is no shortage and no surplus – the market clears.
市场均衡发生在需求量等于供给量的价格水平上。在这一点上，没有短缺也没有过剩——市场出清。
Equilibrium: Qd = Qs
均衡：需求量 = 供给量
If the price is set above equilibrium, a surplus (excess supply) emerges, putting downward pressure on price. If the price is below equilibrium, a shortage (excess demand) appears, driving the price up until equilibrium is restored.
如果价格高于均衡水平，就会产生过剩（超额供给），给价格带来下行压力。如果价格低于均衡水平，就会出现短缺（超额需求），推动价格上升，直到重新恢复均衡。
This automatic adjustment is sometimes called the invisible hand of the market, a term from Adam Smith.
这种自动调节机制有时被称作“看不见的手”，这个术语来自亚当·斯密。
6. Consumer and Producer Surplus | 消费者剩余与生产者剩余
Consumer surplus is the extra benefit consumers receive when they pay a price lower than what they were willing to pay. On a graph it is the area under the demand curve and above the market price.
消费者剩余是指消费者支付的价格低于他们愿意支付的最高价格时所获得的额外收益。在图形上，它是需求曲线之下、市场价格之上的面积。
Consumer Surplus = Willingness to Pay – Market Price
消费者剩余 = 支付意愿 – 市场价格
Producer surplus is the extra benefit producers receive when they sell at a market price higher than the minimum they would accept. It is the area above the supply curve and below the market price.
生产者剩余是指生产者以高于他们愿意接受的最低价格出售商品时所获得的额外收益。它是供给曲线之上、市场价格之下的面积。
Total welfare in a market is the sum of consumer surplus and producer surplus. Free competitive markets aim to maximise this total.
市场中的总福利是消费者剩余与生产者剩余之和。自由竞争市场致力于最大化这一总和。
7. Price Elasticity of Demand (PED) | 需求的价格弹性
Price elasticity of demand measures how responsive the quantity demanded is to a change in price. It is a simple ratio used to predict the effect of price changes on consumer spending.
需求的价格弹性衡量需求量对价格变化的反应程度。它是一个简单的比率，用于预测价格变化对消费者支出的影响。
PED = (% Change in Quantity Demanded) ÷ (% Change in Price)
PED = （需求量变化的百分比）÷（价格变化的百分比）
If PED > 1, demand is elastic – consumers are very sensitive to price. If PED < 1, demand is inelastic – quantity demanded changes little when price changes. Goods with many substitutes tend to have elastic demand; necessities often have inelastic demand.
如果 PED > 1，需求是富有弹性的——消费者对价格非常敏感。如果 PED < 1，需求是缺乏弹性的——价格变动时需求量变化很小。替代品多的商品往往富有弹性；生活必需品通常缺乏弹性。
8. Costs and Revenue | 成本与收益
Understanding costs helps firms decide how much to produce. Total cost includes fixed costs (e.g., rent) and variable costs (e.g., raw materials). Total revenue is the income from sales.
理解成本有助于企业决定生产多少。总成本包括固定成本（如租金）和可变成本（如原材料）。总收益是销售所得的收入。
Total Cost (TC) = Fixed Cost (FC) + Variable Cost (VC)
总成本（TC）= 固定成本（FC）+ 可变成本（VC）
Total Revenue (TR) = Price × Quantity Sold
总收益（TR）= 价格 × 销售数量
Profit is the difference between total revenue and total cost. To break even, a firm must set its price and output so that total revenue equals total cost.
利润是总收益与总成本之间的差额。企业要实现盈亏平衡，必须使总收益等于总成本。
9. Profit Maximisation Rule | 利润最大化法则
Economists say that firms maximise profit where marginal revenue (MR) equals marginal cost (MC). This rule tells them when to stop expanding output.
经济学家认为，当边际收益（MR）等于边际成本（MC）时，企业实现利润最大化。这条规则告诉企业应该何时停止扩大产量。
Profit Max Rule: MR = MC
利润最大化法则：MR = MC
If MR > MC, the extra unit adds more to revenue than to cost, so the firm should produce more. If MR < MC, the extra unit costs more than it brings in, so the firm should cut back output.
如果 MR > MC，额外一单位带来的收入大于增加的成本，企业应扩大生产。如果 MR < MC，额外一单位增加的成本大于带来的收入，企业应减少产出。
10. Taxes and Subsidies | 税收与补贴
Governments use indirect taxes (e.g., VAT) to raise revenue or discourage certain activities, and subsidies to encourage the production and consumption of merit goods.
政府利用间接税（如增值税）来增加财政收入或抑制某些活动，同时利用补贴来鼓励有益品的生产和消费。
A tax shifts the supply curve upwards by the amount of the tax per unit, raising the equilibrium price and reducing the equilibrium quantity.
税收使得供给曲线以每单位税额的幅度向上移动，从而提高均衡价格并减少均衡数量。
A subsidy shifts the supply curve downwards, lowering the price to consumers and increasing the quantity traded. The cost to the government is the subsidy per unit multiplied by the new quantity.
补贴使供给曲线向下移动，降低消费者支付的价格并增加交易数量。政府的成本等于每单位补贴乘以新的数量。
Government Cost of Subsidy = Subsidy per Unit × New Quantity
政府补贴成本 = 每单位补贴额 × 新数量
11. Comparative Advantage and Specialisation | 比较优势与专业化
Comparative advantage exists when a country or individual can produce a good at a lower opportunity cost than another. This is the basis for trade.
比较优势是指一个国家或个人以比另一方更低的机会成本生产某种商品的能力。这是贸易的基础。
Even if one party is absolutely better at producing everything, both can still gain from trade by specialising in the goods where their opportunity cost is lowest.
即使一方在生产所有商品上都具有绝对优势，双方仍然可以通过专注于各自机会成本最低的商品进行贸易而获益。
Gains from trade arise when: Opportunity Cost of Good A in Country X < Opportunity Cost of Good A in Country Y
贸易收益产生于：X国生产商品A的机会成本 < Y国生产商品A的机会成本
Specialisation then allows higher total output, which can be shared through exchange.
专业化能够带来更高的总产出，并通过交换进行分享。
12. Exchange Rates and Simple Currency Conversion | 汇率与简单货币换算
An exchange rate is the price of one currency expressed in another. It allows us to compare prices across countries.
汇率是一种货币以另一种货币表示的价格。它使我们能够比较各国之间的价格。
Amount in Foreign Currency = Amount in Home Currency × Exchange Rate
外币金额 = 本币金额 × 汇率
If £1 = $1.25, then a £20 book costs $20 × 1.25 = $25. When the pound strengthens, imports become cheaper and exports become dearer.
如果1英镑=1.25美元，那么一本价值20英镑的书售价为20 × 1.25 = 25美元。当英镑升值时，进口商品变得更便宜，出口商品变得更昂贵。
This relationship helps explain why governments sometimes care about the value of their currency.
这种关系有助于解释为什么政府有时会关注本国货币的价值。
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