📚 Edexcel Maths for Economics Year 2: Quantitative Methods and Exam Applications | Edexcel 经济学第二年数学：定量方法与考试应用
This revision guide covers the essential quantitative techniques in the second year of Edexcel A-Level Economics. It focuses on calculations, interpretations and exam-style applications that regularly appear in Paper 1, Paper 2 and Paper 3. The goal is to help you move from formula recall to confident numerical analysis under timed conditions.
本复习指南涵盖 Edexcel A-Level 经济学第二年中的核心定量方法。内容集中在计算、解释以及试卷 1、试卷 2 和试卷 3 中经常出现的考试型应用。目标是帮助你从公式记忆提升到限时条件下自信的数值分析。
1. Elasticities: PED, YED, XED and PES | 弹性：需求价格弹性、收入弹性、交叉弹性和供给价格弹性
Price elasticity of demand (PED) measures the responsiveness of quantity demanded to a change in price. It is calculated as the percentage change in quantity demanded divided by the percentage change in price.
需求价格弹性（PED）衡量需求量对价格变化的反应程度。它的计算方法是需求量变化的百分比除以价格变化的百分比。
PED = %ΔQd ÷ %ΔP
demand is unit elastic. PED is usually negative but is often quoted as an absolute value.
解释：如果 PED > 1，需求富有弹性；如果 PED < 1，需求缺乏弹性；如果 PED = 1，需求具有单位弹性。PED 通常为负值，但通常引用其绝对值。
Example: if price rises from £10 to £12 and quantity demanded falls from 100 units to 80 units, then %ΔQd = −20% and %ΔP = 20%, so PED = −20% ÷ 20% = −1. The absolute value is 1, so demand is unit elastic.
示例：如果价格从 10 英镑上升到 12 英镑，需求量从 100 单位下降到 80 单位，那么 %ΔQd = −20%，%ΔP = 20%，所以 PED = −20% ÷ 20% = −1。绝对值为 1，因此需求是单位弹性。
Income elasticity of demand (YED) is %ΔQd ÷ %ΔY, cross elasticity of demand (XED) is %ΔQd of good A ÷ %ΔP of good B, and price elasticity of supply (PES) is %ΔQs ÷ %ΔP.
收入弹性（YED）等于需求量变化的百分比除以收入变化的百分比；交叉弹性（XED）等于商品 A 需求量变化的百分比除以商品 B 价格变化的百分比；供给价格弹性（PES）等于供给量变化的百分比除以价格变化的百分比。
YED = %ΔQd ÷ %ΔY XED = %ΔQd(A) ÷ %ΔP(B) PES = %ΔQs ÷ %ΔP
When calculating these, always express the changes as percentages of the original values, not as absolute differences. Use the midpoint formula only if the question specifically asks for it, but Edexcel normally accepts the simple percentage method.
计算这些弹性时，始终将变化表示为原始值的百分比，而不是绝对差额。除非题目特别要求使用中点公式，否则 Edexcel 通常接受简单百分比方法。
2. Costs of Production and Short-Run Cost Curves | 生产成本与短期成本曲线
Total cost (TC) is the sum of total fixed cost (TFC) and total variable cost (TVC). Average cost (AC) equals total cost divided by output, and marginal cost (MC) equals the change in total cost divided by the change in output.
总成本（TC）是总固定成本（TFC）与总可变成本（TVC）之和。平均成本（AC）等于总成本除以产量，边际成本（MC）等于总成本的变化除以产量的变化。
TC = TFC + TVC AC = TC ÷ Q MC = ΔTC ÷ ΔQ
ost (AVC = TVC ÷ Q). Since AC = TC ÷ Q and TC = TFC + TVC, it follows that AC = AFC + AVC.
你还应该能够计算平均固定成本（AFC = TFC ÷ Q）和平均可变成本（AVC = TVC ÷ Q）。由于 AC = TC ÷ Q 且 TC = TFC + TVC，因此 AC = AFC + AVC。
The short-run cost curves are U-shaped because of the law of diminishing returns. MC cuts AC at the minimum point of the AC curve. Below that point, MC is below AC and pulls AC down; above that point, MC is above AC and pulls AC up.
短期成本曲线呈 U 形，这是边际收益递减规律造成的。边际成本曲线在平均成本曲线的最低点与其相交。在该点以下，MC 低于 AC，并将 AC 拉低；在该点以上，MC 高于 AC，并将 AC 拉高。
Always check whether a cost question is about the short run or the long run. In the short run at least one factor is fixed, so fixed costs exist. In the long run all factors are variable, so no fixed costs exist and firms can experience economies of scale.
务必检查成本问题是关于短期还是长期。在短期中，至少有一种生产要素是固定的，因此存在固定成本。在长期中，所有要素都是可变的，因此不存在固定成本，企业可以经历规模经济。
3. Revenue and Profit Maximisation | 收入与利润最大化
Total revenue (TR) is price multiplied by quantity sold. Average revenue (AR) is total revenue divided by quantity, which equals price. Marginal revenue (MR) is the change in total revenue divided by the change in quantity.
总收入（TR）是价格乘以销售数量。平均收入（AR）是总收入除以数量，等于价格。边际收入（MR）是总收入的变化除以数量的变化。
TR = P × Q AR = TR ÷ Q = P MR = ΔTR ÷ ΔQ
A firm maximises profit where marginal revenue equals marginal cost, provided that MR cuts MC from above. Profit is total revenue minus total cost. At the profit-maximising output, any additional unit would add more to cost than to revenue if output increased, or more to revenue than to cost if output decreased.
企业在边际收入等于边际成本处实现利润最大化，前提是 MR 从上方穿过 MC。利润等于总收入减去总成本。在利润最大化的产量水平上，如果增加产量，每增加一单位带来的成本增加会大于收入增加；如果减少产量，则减少的收入会大于减少的成本。
C. For a monopolist, the demand curve is downward sloping, so price exceeds marginal revenue at every output level.
对于完全竞争企业，价格等于边际收入，因为企业是价格接受者。因此利润最大化发生在 P = MC。对于垄断者，需求曲线向下倾斜，因此在每个产量水平上价格都高于边际收入。
gt; MC at all Q, the firm should continue expanding output until market conditions change.
示例：如果 TR = 12Q，TC = 2Q + 20，那么 MR = 12，MC = 2。由于在所有产量水平上 MR > MC，企业应该继续扩大产量，直到市场条件发生变化。
4. Market Structure: Concentration Ratios and HHI | 市场结构：集中度比率与赫芬达尔指数
Published by TutorHao | Mathematics 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