A-Level Edexcel Economics: Calculation Drill | A-Level Edexcel 经济：计算题专项训练

📚 A-Level Edexcel Economics: Calculation Drill | A-Level Edexcel 经济：计算题专项训练

Calculations form a vital part of Edexcel A-Level Economics papers. This drill targets the key quantitative techniques you must master across microeconomics and macroeconomics to boost your exam performance.

计算题在Edexcel A-Level经济考试中至关重要。本专项训练聚焦于你必须掌握的微观和宏观核心量化技能，帮助你在考试中提升表现。

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1. Price Elasticity of Demand (PED) | 需求价格弹性

PED measures the responsiveness of quantity demanded to a change in price. It is always negative due to the law of demand, but we often use the absolute value.

PED 衡量需求量对价格变化的反应程度。由于需求定律，它总是负值，但我们通常使用绝对值。

The basic formula using percentages: PED = % change in quantity demanded ÷ % change in price.

百分比公式：PED = 需求量变化百分比 ÷ 价格变化百分比。

Edexcel frequently requires the midpoint (arc) formula: PED = (ΔQ / average Q) ÷ (ΔP / average P).

Edexcel 常要求使用中点（弧）公式：PED = (ΔQ / 平均 Q) ÷ (ΔP / 平均 P)。

Example: A shop reduces the price of a jacket from £10 to £8. The quantity demanded rises from 100 to 150 units per week. Calculate PED using the arc method.

例子：某商店将夹克价格从10英镑降至8英镑，每周需求量从100件上升到150件。使用弧法计算PED。

ΔQ = 150 − 100 = 50; average Q = (100 + 150) / 2 = 125.

ΔQ = 150 − 100 = 50；平均 Q = (100 + 150) / 2 = 125。

ΔP = 8 − 10 = −2; average P = (10 + 8) / 2 = 9.

ΔP = 8 − 10 = −2；平均 P = (10 + 8) / 2 = 9。

%ΔQd = (50 / 125) × 100 = 40%. %ΔP = (−2 / 9) × 100 ≈ −22.2%.

%ΔQd = (50 / 125) × 100 = 40%。%ΔP = (−2 / 9) × 100 ≈ −22.2%。

PED = 40% ÷ (−22.2%) ≈ −1.8. Ignoring the sign, PED = 1.8, so demand is price elastic.

PED = 40% ÷ (−22.2%) ≈ −1.8。忽略符号，PED = 1.8，因此需求富有价格弹性。

Elastic demand (PED > 1) means a price cut raises total revenue. In this case, TR rises from £1000 to £1200.

富有弹性 (PED > 1) 意味着降价会增加总收入。本例中，总收入从1000英镑增加到1200英镑。

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2. Income Elasticity of Demand (YED) | 需求收入弹性

YED indicates how quantity demanded responds to a change in consumer income: YED = %ΔQd ÷ %ΔY.

YED 表示需求量对消费者收入变化的反应程度：YED = %ΔQd ÷ %ΔY。

Example: Disposable income grows from £30,000 to £36,000, and demand for organic food increases from 20 kg to 28 kg per household. Find YED.

例子：可支配收入从30,000英镑增加到36,000英镑，有机食品的需求从每户20公斤上升到28公斤。计算YED。

%ΔY = ((36,000 − 30,000) / 30,000) × 100 = 20%. %ΔQd = ((28 − 20) / 20) × 100 = 40%.

%ΔY = ((36,000 − 30,000) / 30,000) × 100 = 20%。%ΔQd = ((28 − 20) / 20) × 100 = 40%。

YED = 40% / 20% = +2.0. This good is a luxury and normal (YED > 1).

YED = 40% / 20% = +2.0。该商品是奢侈品且为正常品 (YED > 1)。

A negative YED would signal an inferior good. A YED between 0 and 1 indicates a necessity.

负的 YED 表示劣等品。YED 介于 0 和 1 之间则为必需品。

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3. Cross Elasticity of Demand (XED) | 需求交叉弹性

XED measures the responsiveness of demand for one good (A) when the price of another good (B) changes: XED = %ΔQd of A ÷ %ΔP of B.

XED 衡量一种商品 (A) 的需求量对另一种商品 (B) 价格变化的反应程度：XED = A商品需求量变化% ÷ B商品价格变化%。

Example: The price of coffee rises from £2.50 to £3.00 per cup, and the demand for tea increases from 500 to 600 cups per day. Calculate XED.

例子：咖啡价格从每杯2.50英镑涨到3.00英镑，茶的需求从每天500杯增加到600杯。计算XED。

%ΔP of coffee = ((3.00 − 2.50) / 2.50) × 100 = 20%. %ΔQd of tea = ((600 − 500) / 500) × 100 = 20%.

咖啡价格变化% = ((3.00 − 2.50) / 2.50) × 100 = 20%。茶需求量变化% = ((600 − 500) / 500) × 100 = 20%。

XED = 20% / 20% = +1.0. The positive sign means coffee and tea are substitutes.

XED = 20% / 20% = +1.0。正号表示咖啡和茶互为替代品。

A negative XED would indicate complementary goods; a value close to zero suggests unrelated products.

负的 XED 表示互补品；数值接近于零则表明产品无关。

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4. Price Elasticity of Supply (PES) | 供给价格弹性

PES captures how quantity supplied responds to price changes: PES = %ΔQs ÷ %ΔP. The arc formula is similar to PED: (ΔQs / average Qs) ÷ (ΔP / average P).

PES 反映供给量对价格变化的反应程度：PES = %ΔQs ÷ %ΔP。弧公式与PED类似：(ΔQs / 平均 Qs) ÷ (ΔP / 平均 P)。

Example: The market price of wheat rises from £150 to £180 per tonne. Quantity supplied increases from 10,000 to 11,500 tonnes. Calculate PES.

例子：小麦市场价格从每吨150英镑涨到180英镑，供给量从10,000吨增加到11,500吨。计算PES。

Average Qs = (10,000 + 11,500) / 2 = 10,750; Average P = (150 + 180) / 2 = 165.

平均 Qs = (10,000 + 11,500) / 2 = 10,750；平均 P = (150 + 180) / 2 = 165。

%ΔQs = (1,500 / 10,750) × 100 ≈ 13.95%. %ΔP = (30 / 165) × 100 ≈ 18.18%.

%ΔQs = (1,500 / 10,750) × 100 ≈ 13.95%。%ΔP = (30 / 165) × 100 ≈ 18.18%。

PES = 13.95% / 18.18% ≈ 0.77. Supply is price inelastic in this range.

PES = 13.95% / 18.18% ≈ 0.77。在此范围内供给缺乏价格弹性。

PES > 1 indicates elastic supply; PES = 1 is unit elastic; PES < 1 is inelastic. The value depends on factors such as time period and spare capacity.

PES > 1 表示供给富有弹性；PES = 1 为单位弹性；PES < 1 缺乏弹性。其值取决于时间周期和闲置产能等因素。

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5. Costs, Revenue and Profit | 成本、收益与利润

Firms need to calculate total cost (TC), average cost (AC), marginal cost (MC), total revenue (TR), marginal revenue (MR) and profit. Key formulas:

企业需要计算总成本 (TC)、平均成本 (AC)、边际成本 (MC)、总收入 (TR)、边际收入 (MR) 和利润。核心公式：

TC = Total Fixed Cost (TFC) + Total Variable Cost (TVC)

TC = 总固定成本 (TFC) + 总可变成本 (TVC)

AC = TC ÷ Q, MC = ΔTC ÷ ΔQ, TR = Price × Q, MR = ΔTR ÷ ΔQ, Profit = TR − TC

AC = TC ÷ Q，MC = ΔTC ÷ ΔQ，TR = 价格 × Q，MR = ΔTR ÷ ΔQ，利润 = TR − TC

Example: A firm has TFC = £40, TVC as shown. The market price is £15 per unit. Complete the table.

例子：某企业TFC = 40英镑，TVC见下表。市场单价为15英镑。请完成表格。

Output Q	TFC (£)	TVC (£)	TC (£)	MC (£)	TR (£)	MR (£)	Profit (£)
0	40	0	40	–	0	–	−40
1	40	10	50	10	15	15	−35
2	40	18	58	8	30	15	−28
3	40	24	64	6	45	15	−19
4	40	32	72	8	60	15	−12
5	40	45	85	13	75	15	−10

MC = change in TC. For Q=1 to 2, ΔTC = 58 − 50 = 8, so MC = 8. MR stays at £15 because the firm is a price taker in perfect competition.

MC = TC的变化量。当Q从1到2，ΔTC = 58 − 50 = 8，因此MC = 8。MR保持15英镑，因为该企业是完全竞争市场中的价格接受者。

Profit is maximised where TR − TC is largest, or where MC ≈ MR (see next section).

利润在 TR − TC 最大（或 MC ≈ MR）时达到最大（见下一节）。

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6. Profit Maximisation: MC = MR | 利润最大化：MC = MR

A firm maximises profit by producing the output where marginal cost equals marginal revenue (MC = MR).

企业通过生产边际成本等于边际收入 (MC = MR)

Published by TutorHao | A-Level Economics Revision Series | aleveler.com

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