📚 Year 8 SQA Economics: Quick Reference to Formulas & Theorems | SQA 八年级经济公式定理速查手册
This handbook provides a concise reference for the fundamental formulas and economic theorems covered in the Year 8 SQA Economics curriculum. Mastering these will help you analyse simple economic problems and prepare for assessments.
本手册为八年级SQA经济课程中所涉及的基本公式和经济定理提供简明参考。掌握这些内容将有助于分析简单的经济问题并为评估做好准备。
1. Opportunity Cost | 机会成本
Opportunity cost is the value of the next best alternative that must be given up when a choice is made. It is a foundational theorem in economics because resources are scarce.
机会成本是当做出选择时必须放弃的次优选项的价值。由于资源是稀缺的，这是经济学的一项基本原理。
Every decision, whether by an individual, a firm, or a government, involves an opportunity cost. For example, if a student spends an hour studying economics instead of playing football, the opportunity cost is the enjoyment and health benefits of the football they gave up.
每一个决策，无论是由个人、企业还是政府作出的，都涉及机会成本。例如，一名学生花了一小时学习经济而不是踢足球，那么机会成本就是他放弃的足球带来的乐趣和健康收益。
The theorem of opportunity cost reminds us that nothing is truly free; even items given away at zero monetary price still require the sacrifice of time or other resources.
机会成本的定理提醒我们，没有什么真正是免费的；即便是以零货币价格赠送的物品，也需要牺牲时间或其他资源。
2. Demand and Quantity Demanded | 需求与需求量
Demand refers to the willingness and ability of consumers to purchase a good or service at various prices over a given period. Quantity demanded is the specific amount consumers are willing to buy at a particular price.
需求是指在一段时期内，消费者在不同价格水平上愿意并能够购买某种商品或服务的总量。需求量则是在某一特定价格下消费者愿意购买的具体数量。
A demand schedule lists quantities demanded at different price points, and a demand curve slopes downward, reflecting the inverse relationship between price and quantity demanded.
需求表列出了不同价格点上的需求量，需求曲线向下倾斜，反映了价格与需求量之间的反向关系。
It is essential to distinguish a movement along the demand curve (caused by a change in price) from a shift in demand (caused by non‑price factors such as income, tastes, or prices of related goods).
区分沿需求曲线的移动（由价格变化引起）与需求的移动（由收入、偏好或相关商品价格等非价格因素引起）至关重要。
3. The 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 other things being equal). Conversely, when price falls, quantity demanded rises.
需求定律指出：在其他条件不变的情况下，一种商品的价格上升，其需求量就会下降。反之，价格下降，需求量上升。
This fundamental theorem works because of the substitution effect and the income effect. If the price of a product increases, consumers switch to relatively cheaper substitutes, and their real purchasing power declines, so they buy less.
这一基本定理之所以成立，是因为替代效应和收入效应。如果产品价格上涨，消费者会转向相对便宜的替代品，其实际购买力下降，因而购买量减少。
Exceptions like Giffen goods (extremely inferior staples) are rare and do not alter the general reliability of the law in everyday markets.
像吉芬商品（极端劣质的主食）这样的例外很罕见，不会改变该定律在日常市场中的普遍可靠性。
4. The 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. When price falls, quantity supplied falls, assuming no other changes.
供给定律指出：在其他条件不变的情况下，一种商品的价格上升，其供给量就会上升。价格下降，供给量则会下降。
This occurs because higher prices increase potential profit margins, motivating producers to allocate more resources to production. A supply curve therefore slopes upward.
这是因为较高的价格提高了潜在利润率，激励生产者将更多资源配置到生产中。因此，供给曲线向上倾斜。
As with demand, changes in the product's own price cause a movement along the supply curve, while shifts in supply are driven by factors like production costs, technology, taxes, or the number of sellers.
与需求类似，产品自身价格的变化引起沿供给曲线的移动，而供给的移动则是由生产成本、技术、税收或卖方数量等因素造成的。
5. Market Equilibrium | 市场均衡
Market equilibrium occurs where the quantity demanded equals the quantity supplied at a given price. This is the market‑clearing price, at which there is no excess supply (surplus) or excess demand (shortage).
市场均衡发生在某一价格水平上需求量等于供给量之时。该价格即为市场出清价格，此时不存在超额供给（过剩）或超额需求（短缺）。
If the market price is above equilibrium, a surplus pushes the price down. If it is below equilibrium, a shortage pushes the price upward. This automatic tendency toward equilibrium is a core theorem of competitive markets.
如果市价高于均衡价格，过剩会令价格下跌；如果市价低于均衡价格，短缺则会推高价格。这种自发趋向均衡的机制是竞争性市场的一个核心定理。
Graphically, equilibrium is found at the intersection of the demand and supply curves. Any external shock that shifts either curve leads to a new equilibrium price and quantity.
从图形上看，均衡即需求曲线与供给曲线的交点。任何导致其中一条曲线移动的外部冲击，都会产生新的均衡价格和数量。
6. Total Revenue Formula | 总收入公式
Total revenue is the income a firm receives from selling its products. It is one of the simplest yet most important calculations in business and economics.
总收入是企业从销售产品中获得的收入。它是商业和经济学中最简单但又最重要的计算之一。
Total Revenue (TR) = Price (P) × Quantity Sold (Q)
总收入 (TR) = 价格 (P) × 销售量 (Q)
For instance, if a bakery sells 200 loaves of bread at £1.50 each, total revenue equals 1.50 × 200 = £ Firms analyse total revenue to understand sales performance and to make pricing decisions.
例如，一家面包店以每条1.50英镑的价格售出200条面包，总收入等于1.50 × 200 = 300英镑。企业分析总收入以了解销售业绩并制定定价决策。
7. Total Cost and Profit | 总成本与利润
Total cost represents all expenses a firm incurs in producing a certain level of output. It is the sum of fixed costs (which do not change with output) and variable costs (which change with output).
总成本代表企业在生产某一产出水平时所发生的一切开支。它是固定成本（不随产出变化）与可变成本（随产出变化）的总和。
Total Cost (TC) = Fixed Cost (FC) + Variable Cost (VC)
总成本 (TC) = 固定成本 (FC) + 可变成本 (VC)
Profit is then determined by comparing total revenue with total cost. A positive figure indicates a gain, while a negative figure is a loss.
利润则由总收入与总成本相比较所得。正数表示盈利，负数则为亏损。
Profit (π) = Total Revenue (TR) − Total Cost (TC)
利润 (π) = 总收入 (TR) − 总成本 (TC)
Understanding these two formulas allows businesses to set targets, control expenses, and evaluate financial sustainability.
理解这两个公式可使企业设立目标、控制开支并评估财务可持续性。
8. Average Cost | 平均成本
Average cost is the cost of producing one unit of output. It helps firms determine whether production is efficient and how to price their products competitively.
平均成本是生产一单位产出的成本。它有助于企业判断生产是否有效率以及如何有竞争力地定价。
Average Cost (AC) = Total Cost (TC) ÷ Quantity (Q)
平均成本 (AC) = 总成本 (TC) ÷ 数量 (Q)
If a company's total cost for producing 500 units is £2,000, the average cost is £2,000 ÷ 500 = £4 per unit. When price exceeds average cost, the firm makes a profit on each unit sold.
如果一家公司生产500单位的总成本为2,000英镑，则平均成本为2,000 ÷ 500 = 每单位4英镑。当价格高于平均成本时，企业售出的每单位产品都能盈利。
9. Price Elasticity of Demand (PED) | 需求价格弹性
Price elasticity of demand measures how responsive quantity demanded is to a change in price. It is expressed as a ratio of percentage changes.
需求价格弹性衡量需求量对价格变化的反应程度，以百分比变化的比率表示。
PED = (%Δ Quantity Demanded) ÷ (%Δ Price)
PED = (需求量变动%) ÷ (价格变动%)
If PED > 1, demand is elastic: consumers are very sensitive to price changes. If PED < 1, demand is inelastic: consumers are less responsive. A PED of exactly 1 is unit elastic.
若PED > 1，需求具有弹性，消费者对价格变化非常敏感；若PED < 1，需求缺乏弹性，消费者反应较小；PED恰好等于1则为单位弹性。
Knowledge of PED helps firms predict how a price increase or decrease will affect their total revenue. For example, raising prices on inelastic goods tends to boost revenue, while the same action on elastic goods may cause a revenue drop.
了解需求价格弹性有助于企业预测提价或降价对总收入的影响。例如，对缺乏弹性的商品提价往往会增加收入，而对富有弹性的商品同样提价则可能导致收入下降。
10. Production and Productivity | 生产与生产率
Production refers to the total output of goods and services. Productivity measures how efficiently inputs are converted into output, typically expressed as output per unit of input.
生产指商品和服务的总产出。生产率衡量投入转化为产出的效率，通常表示为每单位投入的产出量。
Labour Productivity = Total Output ÷ Number of Workers
劳动生产率 = 总产出 ÷ 工人数量
0 = 50 units per worker. Higher productivity can lower average costs and increase a nation's standard of living.
如果10名工人一周生产500个单位，劳动生产率为500 ÷ 10 = 每名工人50个单位。提高生产率可以降低平均成本并提高国民生活水平。
The theorem of diminishing returns warns that adding more of one input, while holding others fixed, will eventually yield smaller increases in output.
收益递减规律警示，在其他投入固定不变的情况下，持续增加一种投入最终会导致产出增量变小。
11. Economies of Scale | 规模经济
Economies of scale refer to the cost advantages that firms obtain as they increase their output in the long run. When a company expands, its long‑run average costs tend to fall, which is an important theorem in production economics.
规模经济是指企业在长期中扩大产出时获得的成本优势。当公司扩张时，其长期平均成本往往会下降，这是生产经济学中的一个重要定理。
Internal economies of scale arise from factors inside the firm, such as technical efficiencies, bulk‑buying discounts, financial advantages, and managerial specialisation. External economies arise from industry‑wide improvements, like better infrastructure or a pool of skilled labour.
内部规模经济源于企业内部因素，如技术效率、批量采购折扣、融资优势和管理专业化。外部规模经济则来自全行业范围内的改善，例如更好的基础设施或熟练劳动力聚集。
However, firms can also experience diseconomies of scale if they become too large and face communication breakdowns or coordination problems.
然而，如果企业规模过大导致沟通失灵或协调问题，也可能出现规模不经济。
12. Marginal Analysis | 边际分析
Marginal analysis examines the additional benefit or cost arising from one extra unit of activity. It is a decision‑making tool used by both firms and consumers.
边际分析考察增加一单位活动所带来的额外收益或成本。它是企业和消费者都使用的决策工具。
Marginal Cost (MC) = Change in Total Cost (ΔTC) ÷ Change in Quantity (ΔQ)
边际成本 (MC) = 总成本的变化 (ΔTC) ÷ 数量的变化 (ΔQ)
The principle of marginal utility explains why the extra satisfaction from consuming one more unit declines as we consume more. This helps shape the downward‑sloping demand curve.
边际效用原理解释了为何随着消费的增加，多消费一单位所带来的额外满足感会递减。这有助于解释需求曲线为何向下倾斜。
In perfectly competitive markets, the profit‑ s may not calculate this point yet, the logic of comparing added costs and added benefits lies at the heart of sound economic reasoning.
在完全竞争市场中，利润最大化的条件是边际成本等于边际收益（MC = MR）。虽然八年级学生可能尚未计算这一均衡点，但比较额外成本与额外收益的逻辑是健全经济推理的核心。
Published by TutorHao | Economics Revision Series | aleveler.com
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