📚 Year 7 SQA Economics: Formula & Theorem Quick Reference Guide | Year 7 SQA 经济：公式定理速查手册
This quick reference handbook covers essential formulas and economic theorems for Year 7 SQA Economics. Each concept is explained clearly with a formula or theorem, paired in English and Chinese, to help you revise efficiently for your assessments.
本速查手册涵盖了 Year 7 SQA 经济学的核心公式与定理。每个概念都配有英文与中文解释，帮助你高效复习备考。
1. Scarcity and Choice | 稀缺性与选择
Scarcity refers to the basic economic problem: finite resources cannot satisfy all human wants. Because resources such as land, labour, and capital are limited, individuals and societies must make choices about how to allocate them.
稀缺性指根本的经济问题：有限的资源无法满足所有人类欲望。由于土地、劳动力、资本等资源是有限的，个人和社会必须就如何分配这些资源做出选择。
Choice involves deciding between alternative uses of scarce resources. Every choice incurs an opportunity cost.
选择涉及在不同用途的稀缺资源之间做出决定。每一次选择都会产生机会成本。
2. Opportunity Cost | 机会成本
Opportunity cost is the value of the next best alternative that is given up when a choice is made. It represents the true cost of any decision.
机会成本是指当做出选择时所放弃的次优选项的价值。它代表了任何决定的真实成本。
Opportunity Cost = Value of Next Best Alternative Foregone
机会成本 = 所放弃的次优选项的价值
For example, if a student chooses to study economics instead of playing sports, the opportunity cost is the enjoyment and health benefits from the sports activity.
例如，如果一名学生选择学习经济学而不是进行体育运动，机会成本就是体育运动带来的乐趣和健康收益。
3. Production Possibility Frontier (PPF) | 生产可能性边界
The PPF shows the maximum possible combinations of two goods or services that an economy can produce with its given resources and technology, assuming full and efficient use of resources.
生产可能性边界（PPF）展示了一个经济体在给定资源和技术条件下，充分利用资源时所能生产的两种商品或服务的最大可能组合。
Points on the PPF are efficient; points inside the PPF are inefficient (unemployment of resources); points outside are unattainable with current resources.
位于 PPF 上的点是有效率的；PPF 内部的点表明资源未充分利用（存在失业）；外部的点在现有资源下无法达到。
Marginal Rate of Transformation (MRT) = ΔY / ΔX
边际转换率（MRT）= ΔY / ΔX
MRT measures the opportunity cost of producing one more unit of X in terms of Y forgone. It is the slope of the PPF.
MRT 衡量多生产一单位 X 所放弃的 Y 的数量，即 PPF 的斜率，代表机会成本。
4. Demand and Law of Demand | 需求与需求定律
Demand is the quantity of a good or service that consumers are willing and able to buy at various prices over a given period, ceteris paribus.
需求是指在其他条件不变的前提下，消费者在一定时期内愿意并且能够购买的商品或服务的数量。
The law of demand states that, ceteris paribus, as the price of a good rises, the quantity demanded falls, and vice versa. This inverse relationship is shown by a downward-sloping demand curve.
需求定律指出，在其他条件不变时，商品价格上升会导致需求量下降，反之亦然。这种反向关系表现为一条向下倾斜的需求曲线。
A simple linear demand function can be written as:
简单的线性需求函数可写作：
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 parameter.
其中 Qd 为需求量，P 为价格，a 为截距（价格为零时的需求量），b 为斜率参数。
5. Supply and Law of Supply | 供给与供给定律
Supply is the quantity of a good or service that producers are willing and able to offer for sale at various prices over a given period, ceteris paribus.
供给是指在其他条件不变的前提下，生产者在一定时期内愿意并且能够出售的商品或服务的数量。
The law of supply states that, ceteris paribus, as the price of a good rises, the quantity supplied increases, and vice versa. This positive relationship results in an upward-sloping supply curve.
供给定律指出，在其他条件不变时，商品价格上升会导致供给量增加，反之亦然。这种正向关系表现为一条向上倾斜的供给曲线。
A typical linear supply function is:
典型的线性供给函数为：
Qs = c + dP
where Qs is quantity supplied, P is price, c is the intercept (quantity supplied when price is zero, often negative or zero), and d is the slope parameter.
其中 Qs 为供给量，P 为价格，c 为截距（价格为零时的供给量，通常为负或零），d 为斜率参数。
6. Market Equilibrium | 市场均衡
Market equilibrium occurs when the quantity demanded equals the quantity supplied at a particular price. This price is called the equilibrium price, and the quantity is the equilibrium quantity.
市场均衡发生在某一价格水平上，需求量等于供给量。该价格称为均衡价格，数量称为均衡数量。
Equilibrium condition: Qd = Qs
均衡条件：Qd =
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