📚 A-Level OCR Economics: Mastering Calculation Questions | A-Level OCR 经济：计算题专项训练
Calculation questions are a fundamental part of A-Level OCR Economics. They require you to handle numerical data, apply economic formulas accurately, and interpret the results to support analysis and evaluation. From elasticities to national income, mastering these calculations not only secures easy marks but also strengthens your chain of reasoning in longer essay questions. This guide provides targeted practice across all key calculation topics in the OCR specification.
计算题是A-Level OCR经济学的基本组成部分。它们要求你处理数值数据，准确运用经济公式，并解读结果以支持分析和评估。从弹性到国民收入，掌握这些计算不仅确保容易得分的题目，还能增强你在长篇论述题中的推理链条。本指南针对OCR考纲中所有关键计算主题提供专项训练。
1. Overview of Calculation Questions in OCR Economics | OCR经济学计算题概述
In the OCR A-Level Economics exams (H460), calculation questions appear in all three papers. They typically carry 2-6 marks each and test your ability to compute, apply and interpret. Common areas include elasticities, costs, revenues, profits, equilibrium prices, the multiplier, index numbers and exchange rates. You must show working clearly and always give appropriate units or significance.
在OCR A-Level经济学考试（H460）中，计算题出现在全部三张试卷中。它们通常每题2–6分，考查你的计算、运用和解读能力。常见领域包括弹性、成本、收益、利润、均衡价格、乘数、指数和汇率。你必须清晰地展示计算步骤，并始终标出适当的单位或经济含义。
A strong method is to memorise the formula, identify the variables, plug in the numbers and then comment on what the result means in the economic context. Using the correct formula is essential; even a small slip can lose marks. Practise with real-world-style numbers to build speed.
一个有效的方法是牢记公式、识别变量、代入数字，然后结合经济背景点评结果的含义。使用正确的公式至关重要；哪怕一个小的失误也可能丢分。用真实风格的数字进行练习以提高速度。
2. Price Elasticity of Demand (PED) | 需求价格弹性（PED）
PED measures the responsiveness of quantity demanded to a change in price. The basic formula is:
PED = %ΔQd ÷ %ΔP
PED衡量需求量对价格变化的反应程度。基本公式为：需求量变动百分比除以价格变动百分比。
To find the percentage changes, use the initial values unless the question specifies the midpoint method. %ΔQd = (Q2 − Q1) ÷ Q1 × 100. %ΔP = (P2 − P1) ÷ P1 × 100. Always ignore the negative sign when interpreting the magnitude; only the absolute value matters for elasticity classification.
计算百分比变化时，除非题目明确要求中点法，否则使用初始值。需求变动百分比 = (Q₂ − Q₁) ÷ Q₁ × 100。价格变动百分比 = (P₂ − P₁) ÷ P₁ × 100。解读弹性大小时忽略负号，只有绝对值决定弹性的分类。
| Price (P) | Quantity Demanded (Qd) |
|---|---|
| 10 | 100 |
| 8 | 150 |
Example: %ΔQd = (150−100)÷100×100 = +50%. %ΔP = (8−10)÷10×100 = −20%. PED = 50% ÷ 20% = 2.5 (absolute value). Since 2.5 > 1, demand is price elastic. A fall in price leads to a more than proportionate rise in quantity demanded, so total revenue increases.
示例：需求变动百分比 = (150−100)÷100×100 = +50%；价格变动百分比 = (8−10)÷10×100 = −20%；PED = 50% ÷ 20% = 2.5（绝对值）。因为2.5 > 1，需求富有价格弹性。价格下降导致需求量以更大比例增加，因此总收益上升。
3. Income Elasticity of Demand (YED) | 需求收入弹性（YED）
YED measures how quantity demanded responds to a change in consumers’ income. The formula is:
YED = %ΔQd ÷ %ΔY
YED衡量需求量如何随消费者收入变化。公式为：需求量变动百分比除以收入变动百分比。
If YED > 0, the good is a normal good. For normal goods, YED > 1 indicates a luxury, while 0 < YED < 1 indicates a necessity. If YED < 0, the good is an inferior good – demand falls as income rises.
若YED > 0，该商品为正常品。对正常品而言，YED > 1代表奢侈品，0 < YED < 1代表必需品。如果YED < 0，则是劣等品——收入上升需求反而下降。
| Income (Y) | Qd |
|---|---|
| 2000 | 50 |
| 2500 | 70 |
Example: %ΔQd = (70−50)÷50×100 = 40%. %ΔY = (2500−2000)÷2000×100 = 25%. YED = 40% ÷ 25% = 1.6. The positive value greater than 1 shows the good is a luxury normal good.
示例：需求量变动百分比 = 40%，收入变动百分比 = 25%，YED = 1.6。正值且大于1说明该商品是奢侈品正常品。
4. Cross Elasticity of Demand (XED) | 需求交叉弹性（XED）
XED measures the responsiveness of demand for good A when the price of related good B changes. The formula is:
XED = %ΔQd of good A ÷ %ΔP of good B
XED衡量商品A的需求量对相关商品B价格变动的反应程度。公式为：商品A需求量变动百分比除以商品B价格变动百分比。
If XED > 0, goods A and B are substitutes. If XED < 0, they are complements. The larger the absolute value, the stronger the relationship. A value close to zero suggests unrelated goods.
如果XED > 0，商品A和B互为替代品。若XED < 0，则为互补品。绝对值越大，关系越强。接近于零则表明商品不相关。
| P of good B | Qd of good A |
|---|---|
| 5 | 80 |
| 6 | 100 |
Example: %ΔQdA = (100−80)÷80×100 = 25%. %ΔP B = (6−5)÷5×100 = 20%. XED = 25% ÷ 20% = +1.25. The positive sign indicates the two goods are substitutes. A 1% rise in the price of B leads to a 1.25% rise in demand for A.
示例：A需求量变动百分比 = 25%，B价格变动百分比 = 20%，XED = +1.25。正号表明两种商品为替代品。B价格每上升1%，A的需求量上升1.25%。
5. Price Elasticity of Supply (PES) | 供给价格弹性（PES）
PES measures the responsiveness of quantity supplied to a change in price. The formula is:
PES = %ΔQs ÷ %ΔP
PES衡量供给量对价格变动的反应程度。公式为：供给量变动百分比除以价格变动百分比。
When PES > 1, supply is elastic; when PES < 1, it is inelastic. A value of 1 indicates unit elasticity. The key determinants include time period, spare capacity and the ease of factor substitution.
当PES > 1时，供给富有弹性；PES < 1，供给缺乏弹性；等于1为单位弹性。关键决定因素包括时间周期、闲置产能和要素替代的难易程度。
| Price | Qs |
|---|---|
| 4 | 200 |
| 5 | 260 |
Example: %ΔQs = (260−200)÷200×100 = 30%. %ΔP = (5−4)÷4×100 = 25%. PES = 30% ÷ 25% = 1.2. Supply is elastic, meaning producers can increase output more than proportionately in response to a price rise.
示例：供给量变动百分比 = 30%，价格变动百分比 = 25%，PES = 1.2。供给富有弹性，表明生产者能够以超过价格上升的比例增加产出。
6. Costs, Revenue and Profit | 成本、收益与利润
Firms regularly face calculation tasks involving total cost (TC), total revenue (TR) and profit. The key formulas are:
TC = TFC + TVC
AC = TC ÷ Q
MC = ΔTC ÷ ΔQ
TR = P × Q
Profit = TR − TC
企业经常需要计算总成本（TC）、总收益（TR）和利润。关键公式：总成本 = 总固定成本 + 总可变成本；平均成本 = 总成本 ÷ 产量；边际成本 = 总成本变化量 ÷ 产量变化量；总收益 = 价格 × 销量；利润 = 总收益 − 总成本。
Profit maximisation occurs where MC = MR, but in OCR calculations you are often asked to compute profit at a given output or to identify the level of output that yields the greatest profit by comparing TR and TC.
利润最大化发生在MC = MR时，但在OCR计算题中，常要求计算特定产量下的利润，或通过比较TR和TC找出利润最大的产量水平。
| Output | TFC (£) | TVC (£) | Price (£) |
|---|---|---|---|
| 10 | 200 | 100 | 50 |
TC = 200 + 100 = £300. TR = 50 × 10 = £500. Profit = 500 − 300 = £200. If output rises to 11 and TC becomes £320, MC = (320−300) ÷ (11−10) = £20.
TC = 200 + 100 = 300英镑。TR = 50 × 10 = 500英镑。利润 = 500 − 300 = 200英镑。若产量增至11，TC变为320英镑，则MC = (320−300) ÷ (11−10) = 20英镑。
7. Break-even Analysis | 盈亏平衡分析
Break-even output is the level of production where total revenue equals total cost. The formula using contribution is:
Break-even output = TFC ÷ (Price − AVC)
盈亏平衡产量是总收益等于总成本时的产量。使用贡献的公式为：盈亏平衡产量 = 总固定成本 ÷ (单价 − 平均可变成本)。
Here, Price − AVC is the contribution per unit, which goes towards covering fixed costs. Once fixed costs are covered, any additional contribution becomes profit.
这里单价减平均可变成本是单位贡献，用于弥补固定成本。一旦固定成本被弥补，额外的贡献就形成利润。
Example: TFC = £10 000, price = £50, AVC = £30. Break-even = 10 000 ÷ (50 − 30) = 500 units. At 500 units, TR = 500 × 50 = £25 000 and TC = TFC + (AVC × Q) = 10 000 + (30 × 500) = £25 000.
示例：TFC = 1万英镑，单价 = 50英镑，AVC = 30英镑。盈亏平衡产量 = 10000 ÷ (50 − 30) = 500单位。在500单位时，TR = 500 × 50 = 2.5万英镑，TC = 10000 + (30 × 500) = 2.5万英镑。
8. Market Equilibrium and Government Intervention | 市场均衡与政府干预
Equilibrium price and quantity are found by setting quantity demanded equal to quantity supplied. For linear functions, solve Qd = Qs. Suppose demand is Qd = 100 − 2P and supply is Qs = −20 + 4P. Set equal: 100 − 2P = −20 + 4P → 120 = 6P → P* = 20, Q* = 100 − 2(20) =
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