📚 A-Level Edexcel Economics: Formula Summary Handbook | A-Level Edexcel 经济：公式汇总手册
Mastering the essential formulas is fundamental to success in A-Level Economics. This handbook compiles every key calculation and equation you are expected to know for the Edexcel specification, covering microeconomics, macroeconomics and international trade. Use it to build your quantitative confidence and ensure you never lose marks on numerical questions.
掌握核心公式是学好 A-Level 经济学的基础。本手册汇总了 Edexcel 考纲要求的所有关键计算和方程，涵盖微观、宏观与国际贸易。用它来培养你的定量分析信心，确保你在数字题上绝不丢分。
1. Elasticity Formulas | 弹性公式
Price elasticity of demand (PED) measures how responsive quantity demanded is to a change in price. It is always negative, but we often refer to its absolute value. The standard formula uses percentage changes, and a PED greater than 1 in absolute terms indicates elastic demand.
需求的价格弹性（PED）衡量需求量对价格变化的反应程度。它总是负值，但我们通常关心其绝对值。标准公式使用百分比变化，绝对值大于 1 表示需求富有弹性。
PED = %ΔQd / %ΔP
A simple rearrangement allows you to calculate PED between two points using the midpoint formula: PED = (ΔQd / Average Qd) ÷ (ΔP / Average P). This avoids inconsistency depending on which point is treated as the starting value.
运用中点公式可以计算两点之间的弹性：PED = (ΔQd / 平均 Qd) ÷ (ΔP / 平均 P)。这避免了因选择不同起点而造成的不一致。
Cross-price elasticity of demand (XED) shows how the demand for one good responds to a change in the price of another. A positive XED means the goods are substitutes; a negative XED means they are complements. The formula compares percentage changes.
需求的交叉弹性（XED）显示一种商品的需求如何对另一种商品的价格变化作出反应。XED 为正表示替代品，为负表示互补品。公式比较的是百分比变化。
XED = %ΔQd of good A / %ΔP of good B
Income elasticity of demand (YED) captures how demand changes with income. A positive YED indicates a normal good, while a negative YED indicates an inferior good. A YED greater than 1 signifies a luxury good.
需求的收入弹性（YED）反映需求如何随收入变化。YED 为正代表正常品，为负代表低档品。YED 大于 1 则表示奢侈品。
YED = %ΔQd / %ΔY
Price elasticity of supply (PES) measures the responsiveness of quantity supplied to a price change. Its value is usually positive and depends on how easily producers can expand output in the short run.
供给的价格弹性（PES）衡量供给量对价格变化的反应程度。它通常为正值，取决于生产者在短期内扩大产出的难易程度。
PES = %ΔQₛ / %ΔP
2. Costs, Revenue and Profit | 成本、收益与利润
Total cost (TC) is the sum of all fixed and variable costs incurred in production. Fixed costs (FC) do not vary with output, while variable costs (VC) change directly with output. Average total cost (ATC) is TC divided by the quantity produced (Q).
总成本（TC）是生产中发生的所有固定成本和可变成本之和。固定成本（FC）不随产量变化，而可变成本（VC）直接随产量变化。平均总成本（ATC）由 TC 除以产量（Q）得出。
TC = FC + VC
ATC = TC ÷ Q
Marginal cost (MC) is the extra cost of producing one more unit. It is calculated as the change in total cost divided by the change in quantity. MC typically falls then rises due to the law of diminishing returns.
边际成本（MC）是多生产一单位产品所增加的额外成本，计算方法为总成本变动量除以产量变动量。由于收益递减规律，MC 通常先降后升。
MC = ΔTC ÷ ΔQ
Average fixed cost (AFC) and average variable cost (AVC) follow: AFC = FC ÷ Q, AVC = VC ÷ Q. Then ATC = AFC + AVC. Understanding these relationships helps you interpret cost curves accurately.
平均固定成本（AFC）和平均可变成本（AVC）的公式为：AFC = FC ÷ Q，AVC = VC ÷ Q。于是 ATC = AFC + AVC。理解这些关系有助于准确解读成本曲线。
Total revenue (TR) is the income a firm receives from selling its output. It is simply price multiplied by quantity sold. Average revenue (AR) equals TR ÷ Q, which is also the price per unit, so AR = P.
总收益（TR）是企业销售产品所得收入，即为价格乘以销量。平均收益（AR）等于 TR ÷ Q，也就是每单位产品的价格，因此 AR = P。
TR = P × Q
AR = TR ÷ Q = P
Profit (π) is the difference between total revenue and total cost. A firm maximises profit where marginal cost equals marginal revenue, provided MC cuts MR from below.
利润（π）是总收益与总成本之间的差额。企业在边际成本等于边际收益处实现利润最大化，且需要 MC 从下方穿过 MR。
π = TR − TC
3. Market Structure: Revenue and Profit Maximisation | 市场结构：收益与利润最大化
Marginal revenue (MR) is the change in total revenue from selling one extra unit. In perfect competition, MR equals AR and price. In imperfect competition, MR lies below AR and the firm faces a downward-sloping demand curve.
边际收益（MR）是出售额外一单位产品带来的总收益变动。在完全竞争下，MR 等于 AR 和价格。在不完全竞争下，MR 低于 AR，企业面临向下倾斜的需求曲线。
MR = ΔTR ÷ ΔQ
The profit-maximising rule (MC = MR) applies to all market structures. For a perfectly competitive firm, profit maximisation reduces to P = MC, because MR = P. For a monopolist, MR is derived from the demand curve.
利润最大化法则（MC = MR）适用于所有市场结构。对完全竞争企业，利润最大化简化为 P = MC，因为 MR = P。对垄断企业，MR 由需求曲线推导得出。
Profit maximisation: MC = MR
Sales revenue maximisation occurs where MR = 0. Revenue maximisation does not guarantee profit, but it may be a managerial objective in firms with separation of ownership and control.
销售收入最大化发生在 MR = 0 处。收入最大化不保证利润，但在所有权与经营权分离的企业中可能成为管理目标。
Normal profit is included in total cost as the minimum return required to keep factors of production in their current use. Supernormal (abnormal) profit arises when TR > TC, including normal profit.
正常利润包含在总成本中，是让生产要素维持当前用途所需的最低回报。当 TR > TC 时出现超常（超额）利润，且已包含正常利润在内。
4. Consumer and Producer Surplus, Efficiency | 消费者与生产者剩余及效率
Consumer surplus is the difference between what consumers are willing to pay and what they actually pay. Graphically, it is the area below the demand curve and above the equilibrium price.
消费者剩余是消费者愿意支付的金额与实际支付金额之差。在图形上，它是需求曲线下方、均衡价格上方的区域。
Producer surplus is the difference between the price producers receive and the minimum price they would accept. It is the area above the supply curve and below the market price.
生产者剩余是生产者收到的价格与它们愿意接受的最低价格之差，即供给曲线上方、市场价格下方的区域。
Consumer Surplus = Willingness to Pay − Price
Producer Surplus = Price − Minimum Acceptable Price
Allocative efficiency occurs where price equals marginal cost (P = MC), because the value consumers place on the last unit equals its opportunity cost. Productive efficiency is achieved when firms produce at the lowest point on the average total cost curve.
配置效率发生在价格等于边际成本（P = MC）时，因为消费者对最后一单位产品的估值等于其机会成本。生产效率则在企业在平均总成本曲线最低点生产时实现。
Welfare can be measured as total surplus = consumer surplus + producer surplus. A competitive equilibrium maximises total surplus in the absence of market failure.
福利可衡量为总剩余 = 消费者剩余 + 生产者剩余。在没有市场失灵的情况下，竞争性均衡使总剩余最大化。
5. Macroeconomic Indicators | 宏观经济指标
The GDP deflator is a broad measure of the price level in the economy. It is calculated as the ratio of nominal GDP to real GDP, multiplied by 100. This allows you to separate changes in output from changes in prices.
GDP 平减指数是衡量经济整体价格水平的广泛指标，计算方法为名义 GDP 与实际 GDP 之比乘以 100。它可以将产出变化与价格变化分离。
GDP Deflator = (Nominal GDP ÷ Real GDP) × 100
Inflation rate is commonly measured using the Consumer Price Index (CPI). The annual inflation rate equals the percentage change in the CPI between two periods. A similar method applies for the Retail Price Index (RPI).
通货膨胀率通常用消费者价格指数（CPI）衡量。年通胀率等于两个时期 CPI 变动的百分比。零售价格指数（RPI）也采用类似方法。
Inflation Rate = (CPI in Year 2 − CPI in Year 1) ÷ CPI in Year 1 × 100
The unemployment rate expresses the number of unemployed people as a percentage of the labour force. The labour force comprises those who are employed plus those actively seeking work.
失业率表示为失业人数占劳动力人口的百分比。劳动力人口包括就业者和积极寻找工作的人。
Unemployment Rate = (Number Unemployed ÷ Labour Force) × 100
Real variables are adjusted for inflation using the formula: Real = (Nominal ÷ Price Index) × 100. This conversion is essential for meaningful comparisons over time, such as real wages or real GDP per capita.
实际变量通过公式：实际值 =（名义值 ÷ 价格指数）× 100 剔除通胀影响。这一换算是进行跨时期有意义比较的关键，例如实际工资或人均实际 GDP。
6. The Multiplier and Aggregate Demand | 乘数与总需求
The multiplier (k) quantifies the final change in national income resulting from an initial change in spending. Its simplest formula depends on the marginal propensity to consume (MPC), which is the fraction of additional income spent.
乘数（k）衡量初始支出变动最终带来的国民收入变动。最简单的公式取决于边际消费倾向（MPC），即额外收入中用于消费的比例。
Multiplier (k) = 1 ÷ (1 − MPC) or k = 1 ÷ MPS
Since MPC + MPS = 1, the multiplier equals the reciprocal of the marginal propensity to save (MPS). A higher MPC leads to a larger multiplier, amplifying the effects of fiscal policy.
由于 MPC + MPS = 1，乘数等于边际储蓄倾向（MPS）的倒数。MPC 越高，乘数越大，从而放大财政政策的效果。
MPC = ΔC ÷ ΔY MPS = ΔS ÷ ΔY
The marginal propensity to tax (MPT) and marginal propensity to import (MPM) reduce the size of the multiplier. A more complete formula includes these leakages: k = 1 ÷ (MPS + MPT + MPM).
边际税收倾向（MPT）和边际进口倾向（MPM）会缩小乘数。更完整的公式包含这些漏出：k = 1 ÷ (MPS + MPT + MPM)。
k = 1 ÷ (MPS + MPT + MPM)
The change in national income is then ΔY = k × ΔJ, where ΔJ represents an initial injection of spending such as government expenditure or investment.
国民收入的变动即为 ΔY = k × ΔJ，其中 ΔJ 代表初始注入的支出，如政府支出或投资。
7. Money and Banking | 货币与银行
The money multiplier shows how an initial deposit can lead to a larger increase in the broad money supply through repeated rounds of lending. Its size depends on the reserve requirement ratio (RRR) set by the central bank or held voluntarily by commercial banks.
货币乘数显示一笔初始存款如何通过多轮贷款创造出更大的广义货币供给。其大小取决于中央银行设定的或商业银行自愿持有的准备金率（RRR）。
Money Multiplier = 1 ÷ Reserve Ratio
If banks hold a 10% reserve ratio, the money multiplier is 10. An initial deposit of £1,000 could ultimately support £10,000 of new money, assuming no cash leakages. In practice, the multiplier is smaller due to households holding cash and banks keeping excess reserves.
若银行持有 10% 的准备金率，货币乘数就是 10。1000 英镑的初始存款最终可支持 10000 英镑的新增货币，前提是无现金漏出。实际上，由于家庭持有现金和银行保留超额准备金，乘数会更小。
The quantity theory of money provides a long-run link between money supply and the price level. The equation MV = PQ (or MV = PY) states that the money supply times the velocity of circulation equals the price level times real output (or nominal GDP).
货币数量论提供了货币供给与价格水平之间的长期联系。方程 MV = PQ（或 MV = PY）表示货币供给乘以流通速度等于价格水平乘以实际产出（或名义 GDP）。
M × V = P × Y
Assuming V and Y are relatively stable in the long run, any increase in M leads to an equal proportional increase in P. This underpins the monetarist explanation of inflation.
假设长期中 V 和 Y 相对稳定，M 的任何增加会导致 P 同比例上升。这构成了货币主义对通货膨胀的解释。
8. International Trade and Exchange Rates | 国际贸易与汇率
The terms of trade index measures a country’s export prices relative to its import prices. An improvement (rise) in the index means a country can buy more imports for a given quantity of exports.
贸易条件指数衡量一国出口价格相对于进口价格的水平。指数改善（上升）意味着给定数量的出口可以购买更多的进口品。
Terms of Trade = (Index of Export Prices ÷ Index of Import Prices) × 100
A real exchange rate adjusts the nominal exchange rate by the ratio of domestic to foreign price levels. It reflects the purchasing power of one currency relative to another and determines a country’s international competitiveness.
实际汇率用国内价格水平与国外价格水平之比调整名义汇率。它反映一种货币相对于另一种货币的购买力，并决定一国的国际竞争力。
Real Exchange Rate = Nominal Exchange Rate × (Domestic Price Level ÷ Foreign Price Level)
The balance of payments must always balance because it is based on double-entry bookkeeping. The current account plus the capital and financial accounts (including net errors and omissions) sum to zero.
国际收支必须总是平衡的，因为它基于复式记账。经常账户加上资本与金融账户（包括净误差与遗漏）之和为零。
Current Account + Capital Account + Financial Account + Net Errors = 0
9. Consumer Choice and Utility | 消费者选择与效用
The equi-marginal principle states that a rational consumer maximises total utility when the marginal utility per pound spent is equal across all goods. This is a core condition for consumer equilibrium.
等边际原则指出，当花在每种商品上的每英镑边际效用相等时，理性消费者实现了总效用最大化。这是消费者均衡的核心条件。
MUₓ ÷ Pₓ = MUᵧ ÷ Pᵧ
If the ratio of marginal utilities differs, the consumer can raise total utility by reallocating spending toward the good providing higher marginal utility per pound. This reallocation continues until the equilibrium condition is restored.
如果边际效用之比不同，消费者可以通过将支出重新分配到每英镑提供更高效用的商品上来提高总效用。这种重新分配将持续到恢复均衡条件为止。
The marginal rate of substitution (MRS) is the rate at which a consumer is willing to exchange one good for another while maintaining the same level of utility. It equals the absolute value of the slope of the indifference curve.
边际替代率（MRS）是消费者在维持相同效用水平下愿意用一种商品交换另一种商品的比率，它等于无差异曲线斜率的绝对值。
MRS = −ΔY ÷ ΔX (along an indifference curve)
At the optimal consumption bundle, the MRS equals the price ratio: MRS = Pₓ ÷ Pᵧ. This tangency condition aligns the consumer’s subjective trade-off with the market trade-off.
在最优消费组合处，MRS 等于价格比：MRS = Pₓ ÷ Pᵧ。这个切点条件使消费者的主观取舍与市场的客观取舍相一致。
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