📚 Year 7 SQA Economics: Quick Reference Handbook of Formulas and Theorems | Year 7 SQA 经济：公式定理速查手册
This handbook provides a rapid review of the essential formulas and key economic concepts you need for Year 7 SQA Economics. Each section pairs a core idea with its mathematical or graphical expression, followed by a concise explanation. Use it to reinforce your understanding before tests and to build a solid foundation for future study.
这本手册为你快速梳理 Year 7 SQA 经济课程中必须掌握的核心公式与基本定理。每个小节都会将关键概念与其数学或图表表达相对应，并配以简要说明。你可以用它来考前巩固，也可以为今后的学习打下扎实基础。
1. The Law of Demand | 需求定律
As the price of a good falls, the quantity demanded by consumers tends to rise, ceteris paribus. This inverse relationship is known as the Law of Demand.
在其他条件不变的情况下，一种商品的价格下降，消费者对该商品的需求量通常会增加。这种反向关系就是需求定律。
It can be stated as: when Price ↑, Quantity Demanded ↓; when Price ↓, Quantity Demanded ↑.
可以表示为：价格上升，需求量下降；价格下降，需求量上升。
P ↑ → Qd ↓ ; P ↓ → Qd ↑
2. The Demand Curve Slope | 需求曲线斜率
A demand curve slopes downward from left to right, reflecting the Law of Demand. The slope shows how much quantity demanded changes per unit change in price.
需求曲线从左向右下方倾斜，体现了需求定律。斜率表示价格每变动一个单位，需求量相应的变化程度。
For a linear demand curve, slope = ΔP / ΔQd. Because ΔP and ΔQd move in opposite directions, the slope is negative.
对于线性需求曲线，斜率 = ΔP / ΔQd。由于 ΔP 和 ΔQd 变动方向相反，斜率为负。
Slope of demand curve = ΔP ÷ ΔQd (< 0)
3. The Law of Supply | 供给定律
As the price of a good rises, the quantity supplied by producers tends to increase, ceteris paribus. This direct relationship is the Law of Supply.
在其他条件不变的情况下，一种商品的价格上升，生产者愿意提供的数量通常会增加。这种正向关系就是供给定律。
It is expressed as: when Price ↑, Quantity Supplied ↑; when Price ↓, Quantity Supplied ↓.
表示为：价格上升，供给量增加；价格下降，供给量减少。
P ↑ → Qs ↑ ; P ↓ → Qs ↓
4. Market Equilibrium | 市场均衡
Market equilibrium occurs where the quantity demanded equals the quantity supplied at a given price. There is no surplus or shortage at this point.
市场均衡发生在某一价格下需求量等于供给量时。此时既无过剩也无短缺。
The equilibrium condition is Qd = Qs. The price at which this happens is the equilibrium price.
均衡条件为 Qd = Qs。使该等式成立的价格就是均衡价格。
Equilibrium: Qd = Qs → Market-clearing price (Pₑ) and quantity (Qₑ)
5. Price Elasticity of Demand (PED) | 需求的价格弹性
PED measures how responsive the quantity demanded is to a change in price. It is calculated using percentage changes.
PED 衡量需求量对价格变动的反应程度，用百分比变化来计算。
PED = %ΔQd ÷ %ΔP
If PED > 1, demand is elastic (consumers are very responsive). If PED < 1, demand is inelastic. If PED = 1, it is unit elastic.
如果 PED > 1，需求富有弹性；如果 PED < 1，需求缺乏弹性；如果 PED = 1，为单位弹性。
Remember to always use the midpoint formula when data on two points is given:
当给定两个点的数据时，记得使用中点公式：
PED = (ΔQd ÷ average Qd) ÷ (ΔP ÷ average P)
6. Price Elasticity of Supply (PES) | 供给的价格弹性
PES measures how responsive quantity supplied is to a change in price. The formula mirrors PED.
PES 衡量供给量对价格变动的反应程度，公式与 PED 类似。
PES = %ΔQs ÷ %ΔP
A PES > 1 indicates elastic supply; PES < 1 indicates inelastic supply. The sign is usually positive because the relationship between price and quantity supplied is direct.
PES > 1 表示供给富有弹性，PES < 1 表示供给缺乏弹性。由于价格与供给量呈正向关系，通常弹性值为正。
7. Total Revenue and Profit | 总收益与利润
Total revenue (TR) is the money a firm receives from selling its goods. It is simply price multiplied by quantity sold.
总收益（TR）是企业通过销售商品获得的全部货币收入，等于价格乘以销售数量。
TR = P × Q
Profit is what remains after all costs are subtracted from total revenue. It is the reward for risk-taking.
利润是总收益减去所有成本后的剩余部分，是对承担风险的回报。
Profit = TR − Total Cost (TC)
If TR > TC, the firm makes a profit. If TR < TC, it makes a loss.
如果 TR > TC，企业盈利；如果 TR < TC，企业亏损。
8. Costs of Production | 生产成本
Total cost (TC) is the sum of all fixed costs (FC) and variable costs (VC). Fixed costs do not change with output, while variable costs do.
总成本（TC）是固定成本（FC）与可变成本（VC）之和。固定成本不随产量变动，可变成本则随产量变动。
TC = FC + VC
Average total cost (ATC) is the cost per unit of output.
平均总成本（ATC）是每单位产量的成本。
ATC = TC ÷ Q
Marginal cost (MC) is the extra cost of producing one more unit.
边际成本（MC）是多生产一单位产品所增加的成本。
MC = ΔTC ÷ ΔQ
9. Break-even Point | 盈亏平衡点
The break-even point is the level of output where total revenue equals total cost. At this point, the firm makes neither a profit nor a loss.
盈亏平衡点是总收益等于总成本时的产量水平。在此点上企业既不盈利也不亏损。
Break-even: TR = TC or P × Q = FC + VC
Break-even output can be found by: Q = FC ÷ (Price − Average Variable Cost). The term (Price − AVC) is called the contribution margin.
盈亏平衡产量计算公式为： Q = FC ÷ (价格 − 平均可变成本)。(价格 − AVC) 称为边际贡献。
Break-even quantity = FC ÷ (P − AVC)
10. The Circular Flow of Income | 收入循环流动
In a simple economy, households provide factors of production (labour, land, capital) to firms and receive income (wages, rent, profit). Firms use these factors to produce goods and services, which households buy with their income. This creates a circular flow.
在一个简单经济体中，家庭向企业提供生产要素（劳动、土地、资本）并获取收入（工资、租金、利润）。企业利用这些要素生产商品与服务，家庭再用收入购买。这就形成了收入的循环流动。
The basic identity is: Y = C + I, where Y is national income, C is consumption spending, and I is investment.
基本恒等式为：Y = C + I，其中 Y 为国民收入，C 为消费支出，I 为投资。
Y = C + I (two-sector model)
This shows that every pound spent becomes someone else’s income, and the flow continues.
这表明每一英镑的支出都会成为他人的收入，循环往复。
11. Government Intervention: Tax and Subsidy | 政府干预：税收与补贴
An indirect tax (e.g., VAT) is added to the price of a good. It shifts the supply curve vertically upward by the amount of the tax.
间接税（如增值税）被加在商品价格上，使供给曲线向上垂直移动相当于税款的距离。
New supply price = Original supply price + Tax per unit
A subsidy is a payment from the government to producers to lower their costs. It shifts the supply curve downward.
补贴是政府支付给生产者以降低其成本的款项，使供给曲线向下移动。
New supply price = Original price − Subsidy per unit
The incidence (who really pays) of the tax depends on the relative elasticities of demand and supply.
税收的最终负担（由谁实际承担）取决于需求与供给的相对弹性。
12. Key Economic Indicators | 关键经济指标
Inflation is the sustained increase in the general price level. It is often measured by the Consumer Price Index (CPI) and calculated as a percentage change.
通货膨胀是指整体物价水平持续上涨，通常用消费者物价指数（CPI）衡量，并以百分比变动计算。
Inflation rate = (CPI current year − CPI previous year) ÷ CPI previous year × 100
Unemployment rate shows the proportion of the labour force that is actively seeking work but cannot find a job.
失业率表示劳动力中正在积极寻找工作但未找到的比例。
Unemployment rate = (Number of unemployed ÷ Labour force) × 100
Economic growth is typically measured by the change in real Gross Domestic Product (GDP).
经济增长通常通过实际国内生产总值（GDP）的变动来衡量。
Real GDP growth = (Real GDP year 2 − Real GDP year 1) ÷ Real GDP year 1 × 100
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