📚 Formula & Theorem Quick Reference Handbook | 公式定理速查手册
This handbook presents fundamental economic formulas and theorems for Year 7 CIE students. Each entry explains a key idea simply, with a formula or law stated clearly, followed by an example. Use it to revise important concepts before exams. Remember: economics is about how people make choices when resources are limited.
本手册为Year 7 CIE学生梳理经济学基本公式与定理。每个条目简明解释核心概念，清晰陈述公式或定律，并附有例子。考前复习重要概念时可以参考。记住：经济学研究的是人们在资源有限时如何作出选择。
1. The Scarcity Principle | 稀缺原理
Scarcity means that there are never enough resources to satisfy all human wants. Because resources are limited, we must make choices. Scarcity is the basic economic problem.
稀缺意味着永远没有足够的资源来满足人类所有的欲望。由于资源有限，我们必须作出选择。稀缺是基本的经济学问题。
The Scarcity Principle states: Unlimited wants + Limited resources → Scarcity → Choice → Opportunity cost.
稀缺原理：无限的欲望 + 有限的资源 → 稀缺 → 选择 → 机会成本。
Example: A student has £10 to spend. She wants a book (£10) and a cinema ticket (£10). She cannot have both because money is scarce.
示例：一个学生有10英镑。她想要一本书（10英镑）和一张电影票（10英镑）。她无法两者兼得，因为金钱是稀缺的。
2. Opportunity Cost Formula | 机会成本公式
Opportunity cost is the next best alternative given up when a choice is made. It is not all the alternatives, only the one you valued most after your choice.
机会成本是在作出选择时所放弃的次优替代选项。不是所有替代选项，只是你在选择之后最看重的那个选项。
The formula for opportunity cost is simply: Opportunity Cost = Value of the next best alternative foregone.
机会成本公式为：机会成本 = 所放弃的次优替代选项的价值。
If the student buys the book, her opportunity cost is the enjoyment of the cinema. If she chooses the cinema, her opportunity cost is the knowledge from the book.
如果学生买了书，她的机会成本就是看电影的乐趣。如果她选择了电影，她的机会成本就是书本带来的知识。
3. The Production Possibility Curve (PPC) Theorem | 生产可能性曲线定理
A PPC shows the maximum combinations of two goods an economy can produce with all resources fully and efficiently used. Points on the curve are efficient; points inside are inefficient; points outside are unattainable.
生产可能性曲线（PPC）展示一个经济体在充分有效利用全部资源时能够生产的两种商品的最大组合。曲线上的点是有效率的；曲线内的点是无效率的；曲线外的点无法实现。
The PPC Theorem: To produce more of one good, an economy must give up some of another good – this is the law of increasing opportunity cost if the curve is bowed outward.
PPC定理：要生产更多的一种产品，经济体必须放弃一些其他产品——如果曲线向外凸出，这就是机会成本递增定律。
Example: A farm can produce apples and pears. Moving from 0 to 10 apples may cost 2 pears, but moving from 30 to 40 apples may cost 10 pears because resources are not equally suited to both goods.
示例：一个农场可以生产苹果和梨。从0个苹果到10个苹果可能放弃2个梨，但从30个到40个苹果可能放弃10个梨，因为资源并不同等适用于两种产品。
4. Law of Demand | 需求定律
The law of demand states: As the price of a good rises, the quantity demanded falls, ceteris paribus (all else being equal). There is an inverse relationship between price and quantity demanded.
需求定律：当商品价格上升时，需求量下降，其他条件不变。价格与需求量之间存在反向关系。
Formula for a linear demand curve: Qd = a - bP Qd is quantity demanded, P is price, a is quantity demanded when P=0, and b is the slope.
线性需求曲线公式：Qd = a - bP，其中Qd为需求量，P为价格，a为P=0时的需求量，b为斜率。
Example: If Qd = 100 – 2P, then at P=10, Qd = 100 – 20 = 80. At P=20, Qd = 60. Demand falls as price rises.
示例：如果 Qd = 100 – 2P，那么在P=10时，Qd = 80；P=20时，Qd = 60。需求随价格上涨而下降。
5. Law of Supply | 供给定律
The law of supply states: As the price of a good rises, the quantity supplied rises, ceteris paribus. There is a direct relationship between price and quantity supplied.
供给定律：当商品价格上升时，供给量增加，其他条件不变。价格与供给量之间存在正向关系。
Formula for a linear supply curve: Qs = c + dP supplied, c is quantity supplied when P=0 (usually negative or zero), and d is the slope.
线性供给曲线公式：Qs = c + dP，其中Qs为供给量，c为P=0时的供给量（通常为负或零），d为斜率。
mple: If Qs = 20 + 3P, at P=5, Qs = 35. At P=10, Qs = 50. Supply increases as price rises.
示例：如果Qs = 20 + 3P，P=5时，Qs = 35；P=10时，Qs = 50。供给随价格上升而增加。
6. Market Equilibrium Theorem | 市场均衡定理
Market equilibrium occurs where quantity demanded equals quantity supplied. At this point, there is no shortage or surplus, and the market clears.
市场均衡发生在需求量等于供给量之处。此时没有短缺或过剩，市场出清。
Equilibrium condition: Qd = Qs. Solve for P* (equilibrium price) and Q* (equilibrium quantity).
均衡条件：Qd = Qs。求解P*（均衡价格）和Q*（均衡数量）。
Using the demand and supply formulas from above: 100 – 2P = 20 + 3P → 80 = 5P → P* = 16, Q* = 100 – 2(16) = 68.
使用上述需求与供给公式：100 – 2P = 20 + 3P → 80 = 5P → P* = 16，Q* = 68。
7. Total Revenue Formula | 总收益公式
Total revenue (TR) is the money a firm receives from selling its goods. It is calculated by multiplying the price per unit by the number of units sold.
总收益（TR）是企业通过销售商品收到的金额。它由单位价格乘以销售数量计算得出。
Formula: TR = P × Q.
公式：TR = P × Q。
Example: A baker sells 200 loaves of bread at £1.50 each. TR = 1.50 × 200 = £300. If the baker raises the price to £2.00 and sells 150 loaves, TR = 2.00 × 150 = £300. Total revenue stayed the same despite the price rise.
示例：面包师以每块1.50英镑出售200块面包。TR = 1.50 × 200 = 300英镑。如果面包师将价格提高到2.00英镑，只卖出150块，TR = 2.00 × 150 = 300英镑。尽管提价，总收益并未改变。
8. Price Elasticity of Demand (PED) Basics | 需求价格弹性基础
Price elasticity of demand measures how much the quantity demanded responds to a change in price. If the response is large, demand is elastic; if small, it is inelastic.
需求价格弹性衡量需求量对价格变动的反应程度。反应大，需求富有弹性；反应小，需求缺乏弹性。
Formula: PED = (% change in Qd) ÷ (% change in P). Ignore the negative sign and take the absolute value.
公式：PED = （需求量变动的百分比）÷ （价格变动的百分比）。忽略负号，取绝对值。
uries). If PED < 1, demand is inelastic (necessities). If PED = 1, demand is unit elastic.
如果PED > 1，需求富有弹性（奢侈品）。如果PED < 1，需求缺乏弹性（必需品）。如果PED = 1，需求为单位弹性。
Example: A 10% price cut for cinema tickets increases attendance by 15%. PED = 15 ÷ 10 = 1.5 > 1, so demand is elastic.
示例：电影票降价10%导致观影人数增加15%。PED = 15 ÷ 10 = 1.5 > 1，因此需求富有弹性。
9. Price Elasticity of Supply (PES) Basics | 供给价格弹性基础
Price elasticity of supply measures how much the quantity supplied changes when price changes. It depends on how easily producers can increase output.
供给价格弹性衡量价格变化时供给量的变化程度。它取决于生产者增加产量的难易程度。
Formula: PES = (% change in Qs) ÷ (% change in P).
公式：PES = （供给量变动的百分比）÷ （价格变动的百分比）。
If PES > 1, supply is elastic (easy to increase production). If PES < 1, supply is inelastic (hard to increase production, e.g., beachfront hotels).
如果PES > 1，供给富有弹性（容易增加产量）。如果PES < 1，供给缺乏弹性（难以增加生产，如海滨酒店）。
Example: A pencil factory can quickly boost output by 20% when price rises by 10%. PES = 20 ÷ 10 = 2 > 1 – supply is elastic.
示例：铅笔厂在价格上升10%时能迅速提高产量20%。PES = 20 ÷ 10 = 2 > 1，供给富有弹性。
10. The Multiplier Effect (Simple Introduction) | 乘数效应（简单介绍）
When new spending enters the economy, it creates income for someone, who then spends part of it, creating more income. The final increase in national income can be larger than the initial spending.
当新支出进入经济时，它为某人创造收入，此人又将其中一部分支出，创造更多收入。国民收入的最终增加可能大于初始支出。
The multiplier formula: Multiplier = 1 ÷ (1 - MPC), where MPC is the marginal propensity to consume (the fraction of extra income spent).
乘数公式：乘数 = 1 ÷ (1 - MPC)，其中MPC是边际消费倾向（额外收入中用于消费的部分）。
Example: If MPC = 0.8, the multiplier = 1 ÷ (1 - 0.8) = 1 ÷ 0.2 = 5. An initial £100 million investment could raise total income by £500 million if all spending stays within the economy.
示例：如果MPC = 0.8，乘数 = 1 ÷ (1 - 0.8) = 1 ÷ 0.2 = 5。1亿英镑的初始投资如果全部留在经济内部，最终可能使总收入增加5亿英镑。
11. The Quantity Theory of Money (Simplified) | 货币数量论（简化版）
The quantity theory of money explains the link between money supply and prices. It is often expressed by the equation of exchange.
货币数量论解释了货币供应与价格之间的联系。通常用交易方程表示。
Equation: MV = PT or MV = PY y of circulation, P = price level, and T (or Y) = number of transactions (or real output).
方程：MV = PT 或 MV = PY，其中M是货币供应量，V是货币流通速度，P是价格水平，T（或Y）是交易数量（或实际产出）。
nal increase in P (inflation). Example: M doubles → P doubles, assuming V and T unchanged.
如果V和T不变，M的增加会导致P同比例上升（通货膨胀）。示例：M翻倍 → P翻倍，假设V和T不变。
12. Cost-Benefit Principle | 成本效益原则
A rational decision-maker compares the extra (marginal) benefits of an action with its extra (marginal) costs. An action should be taken if marginal benefit exceeds marginal cost.
理性的决策者比较某一行动的额外（边际）收益与其额外（边际）成本。如果边际收益大于边际成本，就应该采取该行动。
Decision rule: If MB > MC → do it; if MB < MC → do not do it.
决策规则：如果MB > MC → 做；如果MB < MC → 不做。
Example: A lemonade stand owner finds that selling one more cup brings in £0.50 (MB) but costs £0.30 (MC) for ingredients. Since 0.50 > 0.30, the extra cup should be sold.
示例：柠檬水摊主发现多卖一杯收益0.50英镑（MB），原料成本0.30英镑（MC）。既然0.50 > 0.30，就应该卖出这额外的一杯。
Published by TutorHao | Economics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图