📚 Year 7 AQA Economics: Formula & Theorem Cheat Sheet | Year 7 AQA 经济：公式定理速查手册
This quick reference guide compiles the essential formulas and theorems of the Year 7 AQA Economics syllabus. Mastering these concepts will help you understand how markets work, how prices are determined, and how businesses make decisions. Let's quickly recap the building blocks of economic analysis.
这本速查手册整理了7年级 AQA 经济学课程中的核心公式与定理。掌握这些概念有助于你理解市场如何运作、价格如何形成以及企业如何决策。让我们快速回顾经济分析的基础模块。
1. Scarcity and Opportunity Cost | 稀缺性与机会成本
The fundamental economic problem is scarcity – unlimited wants versus limited resources. Scarcity forces individuals, firms and governments to make choices. Every choice involves an opportunity cost, which is the value of the next best alternative forgone.
基本的经济问题是稀缺性——无限的欲望与有限的资源之间的矛盾。稀缺性迫使个人、企业和政府做出选择。每一次选择都涉及机会成本，即所放弃的次优选择的价值。
The four factors of production – land, labour, capital and enterprise – are all scarce. There is no 'free lunch'; even items given away for zero monetary price carry an opportunity cost because the resources used could have been allocated elsewhere.
生产的四种要素——土地、劳动、资本和企业才能——都是稀缺的。世上没有'免费的午餐'；即便是零货币价格的物品也存在机会成本，因为所使用的资源本可用于其他地方。
Opportunity cost is not merely a money value; it includes time, satisfaction and any other benefit lost. Understanding opportunity cost is the first step in rational economic decision-making.
机会成本不仅仅是货币价值，它还包括失去的时间、满足感以及其他任何利益。理解机会成本是理性经济决策的第一步。
2. The Law of Demand | 需求定律
The law of demand states that, ceteris paribus (all other factors unchanged), as the price of a good increases, the quantity demanded decreases, and as the price falls, the quantity demanded increases. This inverse relationship gives the demand curve a downward slope from left to right.
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。这种反向关系使得需求曲线从左到右向下倾斜。
A demand schedule lists the quantities consumers are willing and able to purchase at various prices. Below is a demand schedule for a standard product, illustrating the law.
需求表列出了消费者在不同价格水平下愿意并能够购买的数量。下表是一种标准产品的需求表，阐明了需求定律。
| Price per unit (£) | Quantity Demanded (units per week) |
|---|---|
| 1.00 | 100 |
| 2.00 | 80 |
| 3.00 | 60 |
| 4.00 | 40 |
| 5.00 | 20 |
Movements along the demand curve are caused only by price changes. Shifts of the entire demand curve are caused by non-price factors such as changes in income, tastes and prices of related goods.
需求曲线上的移动仅由价格变动引起。整个需求曲线的平移则由非价格因素引起，如收入变化、偏好变化以及相关商品价格变化。
3. 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, and as the price falls, the quantity supplied decreases. Producers are motivated by the prospect of higher revenue and profit.
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；价格下降时，供给量减少。生产者受到更高收入和利润前景的激励。
The supply curve slopes upward from left to right. A supply schedule shows the direct relationship between price and quantity supplied.
供给曲线从左到右向上倾斜。供给表显示了价格与供给量之间的正相关关系。
| Price per unit (£) | Quantity Supplied (units per week) |
|---|---|
| 1.00 | 20 |
| 2.00 | 40 |
| 3.00 | 60 |
| 4.00 | 80 |
| 5.00 | 100 |
Shifts in supply occur when factors such as production costs, technology, indirect taxes or subsidies, and the number of sellers change. A rightward shift represents an increase in supply; a leftward shift is a decrease.
当生产成本、技术、间接税或补贴以及卖家数量等因素发生变化时，供给曲线会发生平移。供给曲线右移表示供给增加，左移表示供给减少。
4. Market Equilibrium | 市场均衡
Market equilibrium occurs where the quantity demanded equals the quantity supplied. At this point, there is no tendency for the price to change. The equilibrium price (market-clearing price) and equilibrium quantity are determined by the intersection of the demand and supply curves.
市场均衡发生在需求量等于供给量之处。在这一点上，价格没有变动的趋势。均衡价格（市场出清价格）和均衡数量由需求曲线和供给曲线的交点决定。
If the current price is above equilibrium, there is excess supply (a surplus). Producers will lower prices to clear unsold stock, moving the market back toward equilibrium. If the price is below equilibrium, excess demand (a shortage) exists, and competition among buyers pushes the price upward.
如果当前价格高于均衡价格，就会出现超额供给（过剩）。生产者会降低价格以清空未售库存，推动市场恢复均衡。若价格低于均衡价格，则存在超额需求（短缺），购买者之间的竞争会抬高价格。
The free operation of demand and supply in competitive markets acts as a self-correcting mechanism. Government interventions such as price floors or ceilings can disrupt this adjustment and create persistent surpluses or shortages.
在竞争性市场中，供需的自由运作起到了自我修正的作用。政府干预如价格下限或上限会扰乱这种调整，导致持续的过剩或短缺。
5. Consumer and Producer Surplus | 消费者剩余与生产者剩余
Consumer surplus measures the welfare that consumers gain from buying a good at a market price lower than their maximum willingness to pay. It is the difference between the total amount consumers are prepared to pay and the amount they actually pay.
消费者剩余衡量消费者以低于其最高支付意愿的市场价格购买商品所获得的福利。它是消费者愿意支付的总金额与实际支付金额之间的差额。
Consumer Surplus = Willingness to Pay - Market Price
On a demand-supply diagram, consumer surplus is the area below the demand curve and above the market price line. Producer surplus is the benefit producers receive by selling at a market price higher than the minimum price they would accept. It is the area above the supply curve and below the market price line.
在供需图中，消费者剩余是需求曲线以下、市场价格线以上的区域。生产者剩余是生产者以高于其最低可接受价格的市场价格销售所获得的收益，即供给曲线以上、市场价格线以下的区域。
Producer Surplus = Market Price - Minimum Supply Price
Total economic surplus is the sum of consumer and producer surplus. In a competitive equilibrium, total surplus is maximised, indicating allocative efficiency.
总经济剩余是消费者剩余与生产者剩余之和。在竞争性均衡中，总剩余达到最大，表明实现了分配效率。
6. Price Elasticity of Demand (PED) | 需求的价格弹性 (PED)
Price elasticity of demand measures the responsiveness of quantity demanded to a change in price. The formula for PED is:
需求的价格弹性衡量需求量对价格变化的反应程度。PED 的计算公式为：
PED = % change in quantity demanded ÷ % change in price
y PED is usually negative, but economists often ignore the minus sign and consider the absolute value. If |PED| > 1, demand is price elastic – a small price change causes a proportionally larger change in quantity demanded. If |PED| < 1, demand is price inelastic. If |PED| = 1, demand is unit elastic. If |PED| = 0, demand is perfectly inelastic (vertical demand curve); if |PED| approaches infinity, demand is perfectly elastic (horizontal demand curve).
PED 通常为负值，但经济学家通常忽略负号，只看绝对值。若 |PED| > 1，需求是富有弹性的——价格微小变化导致需求量更大比例的变化。若 |PED| < 1，需求缺乏弹性。若 |PED| = 1，需求为单位弹性。若 |PED| = 0，需求完全无弹性（垂直需求曲线）；若 |PED| 趋于无穷，需求完全弹性（水平需求曲线）。
Factors influencing PED include the availability of close substitutes, whether the good is a necessity or a luxury, the proportion of income spent on the good, and the time period considered. PED is vital for business revenue decisions: when demand is elastic, lowering price can increase total revenue; when inelastic, raising price can increase total revenue.
影响 PED 的因素包括相近替代品的可得性、商品是必需品还是奢侈品、该商品在收入中的支出比例以及所考虑的时间跨度。PED 对企业的收入决策至关重要：当需求富有弹性时，降价可能增加总收入；当缺乏弹性时，提价可能增加总收入。
7. Price Elasticity of Supply (PES) | 供给的价格弹性 (PES)
Price elasticity of supply measures the responsiveness of quantity supplied to a change in price. Its formula is analogous to PED:
供给的价格弹性衡量供给量对价格变化的反应程度。其公式与 PED 类似：
PES = % change in quantity supplied ÷ % change in price
is inelastic; if PES = 1, supply is unit elastic. Perfectly inelastic supply (PES = 0) means quantity supplied does not respond to price changes, while perfectly elastic supply (PES approaching infinity) means any amount will be supplied at a given price.
与 PED 不同，PES 通常为正，因为价格与供给量同向变动。若 PES > 1，供给是弹性的；若 PES < 1，供给缺乏弹性；若 PES = 1，供给为单位弹性。完全无弹性的供给（PES = 0）意味着供给量不随价格变化；完全弹性的供给（PES 趋于无穷）意味着在给定价格下可供应任意数量。
Key determinants of PES are the time frame, the flexibility of the production process, the availability of spare capacity, and the ease of storing inventory. Supply tends to be more elastic in the long run as firms can adjust all factors of production.
决定 PES 的关键因素包括时间期限、生产过程的灵活性、闲置产能的可用性以及储存库存的难易程度。在长期中，由于企业可以调整所有生产要素，供给通常更具弹性。
8. Costs of Production | 生产成本
Firms incur costs when producing goods and services. Total cost (TC) is the sum of total fixed costs (TFC) and total variable costs (TVC). Fixed costs do not change with output (e.g. rent, salaries of permanent staff), while variable costs change directly with the level of production (e.g. raw materials, energy).
企业在生产商品和服务时会产生成本。总成本 (TC) 是总固定成本 (TFC) 与总可变成本 (TVC) 之和。固定成本不随产量变化（如租金、长期员工的工资），而可变成本直接随生产水平变化（如原材料、能源）。
TC = TFC + TVC
Average total cost (ATC) is the cost per unit of output. Marginal cost (MC) is the additional cost of producing one more unit. These help firms decide the most efficient level of output.
平均总成本 (ATC) 是每单位产量的成本。边际成本 (MC) 是多生产一单位产品所增加
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