📚 IGCSE Economics: Calculation Practice Drills | IGCSE 经济：计算题专项训练
In IGCSE Economics, quantitative questions test your ability to apply formulas, interpret data, and perform calculations accurately. Mastering these numerical skills can secure valuable marks on structured papers. This revision guide provides targeted drills on key calculation topics, with step-by-step solutions and paired English–Chinese explanations to reinforce understanding.
在IGCSE经济学中，计算题考查你应用公式、解读数据并准确运算的能力。掌握这些量化技能可以为结构化试题锁定宝贵分数。本复习指南针对核心计算专题提供专项训练，配有逐步解答和英中对照讲解，以强化理解。
1. Price Elasticity of Demand (PED) | 需求价格弹性 (PED)
Price elasticity of demand measures how much the quantity demanded of a good responds to a change in its price. The basic formula is:
需求价格弹性衡量一种商品的需求量对其价格变化的反应程度。基本公式为：
PED = (% Change in Quantity Demanded) ÷ (% Change in Price)
To calculate percentage changes, use the midpoint method or the simple percentage change method: %ΔQ = [(Q1 − Q0) / Q0] × 100. Remember to ignore the negative sign and interpret the absolute value.
计算百分比变化时，可使用中点法或简单百分比法：%ΔQ = [(Q1 − Q0) / Q0] × 100。记住要忽略负号，并用绝对值进行解释。
Example: The price of a smartphone falls from $800 to $600. As a result, quantity demanded rises from 2 000 units to 3 000 units per month. Calculate PED.
例题：一部智能手机的价格从800美元降至600美元，需求量从每月2000台上升到3000台。计算PED。
Solution: %ΔPrice = [(600 − 800) / 800] × 100 = −25%. %ΔQd = [(3000 − 2000) / 2000] × 100 = +50%. PED = 50% / 25% = 2.0 (ignoring signs). Since PED > 1, demand is price elastic.
解答：价格变化百分比 = [(600 − 800) / 800] × 100 = −25%。需求量变化百分比 = [(3000 − 2000) / 2000] × 100 = +50%。PED = 50% / 25% = 2.0（忽略符号）。因PED > 1，需求富有价格弹性。
2. Price Elasticity of Supply (PES) | 供给价格弹性 (PES)
Price elasticity of supply quantifies the responsiveness of quantity supplied to a change in price. The formula is:
供给价格弹性量化了供给量对价格变化的反应程度。公式为：
PES = (% Change in Quantity Supplied) ÷ (% Change in Price)
If PES > 1, supply is elastic; if PES < 1, supply is inelastic. Factors such as production time and spare capacity influence PES.
如果PES > 1，供给富有弹性；如果PES < 1，供给缺乏弹性。生产时间和闲置产能等因素会影响PES。
Example: The market price of wheat rises from £150 to £180 per tonne. Farmers increase output from 10 000 tonnes to 11 500 tonnes. Compute PES.
例题：小麦的市场价格从每吨150英镑涨至180英镑，农民将产量从10 000吨增加到11 500吨。计算PES。
Solution: %ΔPrice = [(180 − 150) / 150] × 100 = 20%. %ΔQs = [(11 500 − 10 000) / 10 000] × 100 = 15%. PES = 15% / 20% = 0.75. Supply is inelastic.
解答：价格变化百分比 = [(180 − 150) / 150] × 100 = 20%。供给量变化百分比 = [(11 500 − 10 000) / 10 000] × 100 = 15%。PES = 15% / 20% = 0.75。供给缺乏弹性。
3. Income Elasticity of Demand (YED) | 需求收入弹性 (YED)
Income elasticity of demand indicates how demand for a good changes as consumer income changes. The formula is:
需求收入弹性表明商品需求如何随消费者收入变化而变化。公式为：
YED = (% Change in Quantity Demanded) ÷ (% Change in Income)
For normal goods, YED is positive (luxuries have YED > 1, necessities 0 < YED < 1). Inferior goods have negative YED.
对于正常商品，YED为正（奢侈品YED > 1，必需品 0 < YED < 1）。劣等品的YED为负值。
Example: Average household income rises from $40 000 to $44 000 per year. Demand for restaurant meals increases by 12%. Calculate YED and classify the good.
例题：家庭年均收入从40 000美元上升到44 000美元，餐厅用餐的需求增加了12%。计算YED并判断商品类别。
Solution: %ΔIncome = [(44 000 − 40 000) / 40 000] × 100 = 10%. YED = 12% / 10% = 1.2. Since YED > 1, eating out is a luxury good.
解答：收入变化百分比 = [(44 000 − 40 000) / 40 000] × 100 = 10%。YED = 12% / 10% = 1.2。因YED > 1，外出用餐属于奢侈品。
4. Cross Elasticity of Demand (XED) | 需求交叉弹性 (XED)
Cross elasticity of demand measures the responsiveness of demand for one good (A) to a change in the price of another good (B). The formula is:
需求交叉弹性衡量一种商品(A)的需求对另一种商品(B)价格变化的反应程度。公式为：
XED = (% Change in Qd of Good A) ÷ (% Change in Price of Good B)
A positive XED indicates substitutes; a negative XED indicates complements. A value near zero suggests no relationship.
XED为正表示替代品；XED为负表示互补品。接近零表示商品间无关联。
Example: The price of coffee increases by 10%, and the demand for tea rises by 8%. Calculate XED and state the relationship.
例题：咖啡价格上涨10%，茶叶需求增加8%。计算XED并说明两者关系。
Solution: XED = +8% / +10% = +0.8. Since XED is positive, tea and coffee are substitutes.
解答：XED = +8% / +10% = +0.8。因XED为正，茶和咖啡是替代品。
5. Total Revenue and Profit | 总收益与利润
Total revenue (TR) is the income a firm receives from selling its output. It is calculated as price multiplied by quantity sold. Profit is the difference between total revenue and total cost (TC).
总收益(TR)是企业从销售产出中获得的收入，等于价格乘以销售量。利润是总收益与总成本(TC)的差额。
TR = Price × Quantity Profit = TR − TC
Example: A firm sells 4 000 units at $25 each. Total costs are $70 000. Find TR and profit.
例题：某企业以每件25美元的价格销售4000件产品，总成本为70 000美元。求总收益和利润。
Solution: TR = 25 × 4 000 = $100 000. Profit = 100 000 − 70 000 = $30 000.
解答：TR = 25 × 4 000 = 100 000美元。利润 = 100 000 − 70 000 = 30 000美元。
6. Average and Marginal Cost | 平均成本与边际成本
Average total cost (ATC) is the total cost per unit of output. Marginal cost (MC) is the extra cost of producing one more unit. These help firms decide on the optimal output level.
平均总成本(ATC)是每单位产出的总成本。边际成本(MC)是多生产一单位产品所增加的成本。它们帮助企业确定最优产量。
ATC = TC ÷ Q MC = ΔTC ÷ ΔQ
Example: A factory’s total cost rises from $8 000 to $8 600 when output increases from 200 to 250 units. Compute MC and the new ATC.
例题：一家工厂的产量从200单位增加到250单位时，总成本从8 000美元升至8 600美元。计算MC和新的ATC。
Solution: ΔTC = 8 600 − 8 000 = $600. ΔQ = 50. MC = 600 / 50 = $12. New ATC = 8 600 / 250 = $34.40.
解答：总成本变化 = 8 600 − 8 000 = 600美元。产量变化 = 50。MC = 600 / 50 = 12美元。新ATC = 8 600 / 250 = 34.40美元。
7. Opportunity Cost | 机会成本
Opportunity cost is the value of the next best alternative forgone when a choice is made. It is a fundamental concept in economics and can be expressed in numerical terms.
机会成本是做出一项选择时所放弃的次优选项的价值。这是经济学的基本概念，并且可以用数字表示。
Example: A government has a $10 million budget. It can either build a hospital (benefit valued at $15 million) or a sports complex (benefit valued at $12 million). What is the opportunity cost of building the hospital?
例题：某政府有1000万美元预算，可以修建一家医院（收益估值1500万美元）或一个体育中心（收益估值1200万美元）。修建医院的机会成本是多少？
Solution: The next best alternative is the sports complex, valued at $12 million in benefits. Therefore, the opportunity cost of the hospital is the $12 million forgone.
解答：次优替代选项是体育中心，其收益为1200万美元。因此，修建医院的机会成本是放弃的1200万美元。
8. Inflation Rate Using CPI | 用消费者物价指数(CPI)计算通胀率
The inflation rate measures the percentage increase in the general price level over a period, commonly using the Consumer Price Index (CPI). The formula is:
通胀率衡量一段时间内总体物价水平的百分比增长，通常使用消费者物价指数(CPI)。公式为：
Inflation Rate = [(CPIcurrent − CPIprevious) / CPIprevious] × 100
Example: The CPI for 2023 is 126 and for 2022 was 120. Calculate the annual inflation rate for 2023.
例题：2023年的CPI为126，2022年为120。计算2023年的年通胀率。
Solution: Inflation rate = [(126 − 120) / 120] × 100 = (6 / 120) × 100 = 5%.
解答：通胀率 = [(126 − 120) / 120] × 100 = (6 / 120) × 100 = 5%。
9. Unemployment Rate | 失业率
The unemployment rate is the percentage of the labour force that is unemployed and actively seeking work. The labour force includes both employed and unemployed individuals.
失业率是劳动力中失业且正在积极寻找工作的人口所占的百分比。劳动力包括就业者和失业者。
Unemployment Rate = (Number of Unemployed ÷ Labour Force) × 100
Example: In an economy, there are 1.5 million unemployed people and the labour force is 30 million. Find the unemployment rate.
例题：某经济体中失业人口为150万，劳动力总数为3000万。求失业率。
Solution: Unemployment rate = (1.5 million / 30 million) × 100 = 5%.
解答：失业率 = (150万 / 3000万) × 100 = 5%。
10. Exchange Rate Conversions | 汇率换算
Exchange rates allow you to convert one currency into another. If you know the rate, multiply or divide accordingly. For example, if £1 = $1.25, then to find how many dollars you get for a given amount of pounds, multiply by 1.25.
汇率让你可以将一种货币兑换成另一种。如果知道了汇率，相应地进行乘法或除法计算。例如，若£1 = $1.25，那么要将一定金额的英镑换算为美元，乘以1.25即可。
Example: A UK firm exports goods worth £200 000 to the US. The exchange rate is £1 = $1.30. How much does the US importer pay in dollars?
例题：一家英国企业向美国出口价值200 000英镑的货物，汇率为£1 = $1.30。美国进口商需要支付多少美元？
Solution: Dollars = £200 000 × 1.30 = $260 000.
解答：美元金额 = 200 000 × 1.30 = 260 000美元。
If a US tourist converts $1 000 into pounds at the same rate, she receives $1 000 / 1.30 ≈ £769.23.
如果一位美国游客按同样汇率将1 000美元兑换成英镑，她将得到1 000 / 1.30 ≈ 769.23英镑。
11. Tax Incidence and Burden Sharing | 税收归宿与负担分担
When an indirect tax is imposed on a good, the tax burden is shared between consumers and producers. The consumer burden is the increase in the market price paid by buyers; the producer burden is the decrease in the net price received by sellers. The sum of both equals the tax per unit.
当对一种商品征收间接税时，税负由消费者和生产者共同承担。消费者负担是买方支付的市场价格上涨部分；生产者负担是卖方获得的净价格下降部分。两者之和等于每单位税额。
Tax per unit = Consumer Burden + Producer Burden
Example: The original equilibrium price of a pack of cigarettes is $5. The government imposes a tax of $2 per pack. The new market price rises to
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