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曼昆《经济学原理（微观经济学分册）》（第6版）第5章 弹性及其应用课后习题详解跨考网独家整理最全经济学考研真题，经济学考研课后习题解析资料库，您可以在这里查阅历年经济学考研真题，经济学考研课后习题，经济学考研参考书等内容，更有跨考考研历年辅导的经济学学哥学姐的经济学考研经验，从前辈中获得的经验对初学者来说是宝贵的财富，这或许能帮你少走弯路，躲开一些陷阱。
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一、概念题1．弹性（elasticity ）答：弹性指作为因变量的经济量的相对变化对作为自变量的经济变量的相对变化的反应程度或灵敏程度。
弹性用来表明两个经济变量变化的关系，当两个经济变量之间存在函数关系时，作为自变量的经济变量的变化，必然引起作为因变量的经济变量的变化。
弹性的大小由弹性系数来表示，弹性系数等于因变量的相对变化对自变量的相对变化的比值。
即：=因变量的变动比例弹性系数自变量的变动比例设两个经济变量之间的函数关系为()Y f X =，则具体的弹性公式为：YY X Y E X X YX∆∆==⋅∆∆ 其中，E 为弹性系数；X ∆、Y ∆分别为变量X 、Y 的变动量。
弹性概念在西方经济学中广泛应用，经济理论中有多种多样的弹性概念，例如，需求价格弹性、需求收入弹性、供给价格弹性等等。
由于弹性是两个量的相对变化的比，因此，弹性是一个具体的数字，它与自变量和因变量的度量单位无关。
2．需求价格弹性（elasticity of demand ）（华南理工大学2009研）答：需求价格弹性指某种商品需求量变动的百分比与价格变动的百分比之比，它用来衡量商品需求量变动对于商品自身价格变动的敏感程度。
用公式表示为：=需求变动的百分比需求价格弹性价格变动的百分比需求价格弹性的经济含义可表示为“当价格变化百分之一时，需求量可能会有百分之几的变化”。
这一概念是由马歇尔在解释价格与需求的关系时提出的。
第5章弹性及其应用内容提要：需求价格弹性衡量的是需求量对价格变量的反应程度。
如果某种物品可以得到相近的替代品，是奢侈品而不是必需品，市场范围狭小，或者买者有相当长的时间对价格变动做出反应，那么，这种物品就倾向于更富有弹性。
可以用需求量变动百分比除以价格变动百分比来计算需求价格弹性。
如果需求量变动比例小于价格变动比例，那么弹性小于1，就可以说需求缺乏弹性。
如果需求量变动比例大于价格变动比例，那么弹性大于1，就可以说需求富有弹性。
总收益，即对一种物品的总支付量，等于该物品的价格乘以销售量。
对于缺乏弹性的需求曲线，其总收益随着价格的上升而增加；对于富有弹性的需求曲线，其总收益随着价格的上升而减少。
需求收入弹性衡量的是需求量对消费者收入变动的反应程度。
需求的交叉价格弹性衡量一种物品需求量对另一种物品价格变动的反应程度。
供给价格弹性衡量的是供给量对价格变动的反应程度。
这种弹性往往取决于所考虑的时间长短。
在大多数市场上，供给在长期中比在短期中更富有弹性。
可以用供给量变动百分比除以价格变动百分比来计算供给价格弹性。
如果供给量变动比例小于价格变动比例，那么弹性小于1，就可以说供给缺乏弹性。
如果供给量变动比例大于价格变动比例，那么弹性大于1，就可以时候供给富有弹性。
供给工具可以被运用于许多不同种类的市场。
小麦市场、石油市场、非法毒品市场。
关键概念：弹性：衡量需求量或供给量对其某种决定因素的反应程度的指标。
富有价格弹性：衡量一种物品需求量对其价格变动反应程度的指标。
用需求量变动百分比除以价格变动百分比来计算。
总收益：一种物品的买者支付从而卖者得到的量，用该物品的价格乘以销售量来计算。
需求收入弹性：衡量一种物品需求量对消费者收入变动反应程度的指标，用需求量变动百分比除以收入变动百分比来计算。
需求的交叉价格弹性：衡量一种物品需求量对另一种物品价格变动的反应程度的指标，用第一种物品需求量变动百分比除以第二种物品价格变动百分比来计算。
《经济学原理》第五章弹性及其应用在本章中你将——了解需求弹性的含义考察决定需求弹性的因素是什么了解供给弹性的含义考察决定供给弹性的因素是什么在三个专门不同的市场上运用弹性的概念上一章中介绍了供给与需求。
在任何一个竞争市场上，例如小麦市场，向右上方倾斜的供给曲线代表卖者的行为，而向右下方倾斜的需求曲线代表买者的行为。
一种物品价格的调整使该物品的需求量与供给量实现平稳。
为了运用这种差不多分析来讲明农业科学家发觉的阻碍，我们必须第一提出另一种工具：弹性的概念。
弹性是衡量买者与卖者对市场条件变动反应大小的指标，它使我们能够更精确地分析供给与需求。
需求弹性需求价格弹性及其决定因素需求规律讲明，一种物品的价格下降使需求量增加。
需求价格弹性衡量需求量对价格变动的反应程度，是一种物品需求量对其价格变动反应程度的衡量，用需求量变动的百分比除以价格变动的百分比来运算。
假如一种物品的需求量对价格变动的反应大，能够讲这种物品的需求是富有弹性的。
假如一种物品的需求量对价格变动的反应小，能够讲这种物品的需求是缺乏弹性的。
什么因素决定一种物品的需求富有弹性依旧缺乏弹性呢? 由于任何一种物品的需求取决于消费者的偏好，因此，需求的价格弹性取决于许多形成个人欲望的经济、社会和心理因素。
然而，依照体会，我们能够讲出某些决定需求价格弹性的一样规律。
必需品与奢侈品必需品倾向于需求缺乏弹性，而奢侈品倾向于需求富有弹性。
当看病的价格上升时，尽管人们会比平常看病的次数少一些，但可不能大幅度地改变他们看病的次数。
与此相比，当游艇价格上升时，游艇需求量会大幅度减少。
缘故是大多数人把看病作为必需品，而把游艇作为奢侈品。
因此，一种物品是必需品依旧奢侈品并不取决于物品本身固有的性质，而取决于买者的偏好。
关于一个热衷于航行而不太关注自己健康的水手来讲，游艇可能是需求缺乏弹性的必需品，而看病是需求富有弹性的奢侈品。
相近替代品的可获得性有相近替代品的物品往往较富有需求弹性，因为消费者从这种物品转向其他物品较为容易。
第5章弹性及其应用①需求弹性弹性(elasticity)：需求量或供应量对其决定因素的响应程度需求价格弹性(price elasticity of demand)：需求量对价格的响应程度，决定因素如下：1.有相近替代物的商品需求弹性大2.必需品需求弹性小，奢侈品需求弹性大3.市场越狭义(如香草味冰淇淋)弹性越大4.时间跨度越大弹性越大需求价格弹性=需求量的变化百分比/价格变化百分比为避免基准点不同引起不同，常用中值法：需求价格弹性=(Q2-Q1)/[(Q2+Q1)/2](P2-P1)/[(P1+P2)/2]总收益(total revenue)=P×Q需求曲线越平缓弹性越大，曲线竖直为完全无弹性(perfectly elastic)，水平为完全有弹性(perfectly elastic)，需求价格弹性大于1为弹性大(elastic)，价格与总收益成负相关，小于1为弹性小(inelastic)，价格与总收入成正相关，等于1为单位弹性(unit elastic)，总收益不随价格变化线型的需求曲线斜率不变，但弹性随价格升高而增大需求收入弹性(income elasticity of demand)=需求量变化百分比/收入变化百分比需求交叉价格弹性(cross-price elasticity of demand)=a物品需求量变化百分比/b物品价格变化百分比②供应弹性供应价格弹性(price elasticity of supply)：供应量对价格的响应程度，与货物本身属性有关，且时间越长弹性越大供应价格弹性=供应量的变化百分比/价格变化百分比供应曲线越平缓弹性越大，曲线竖直为完全无弹性，水平为完全有弹性，供应价格弹性大于1为弹性大，小于1为弹性小，等于1为单位弹性③应用例1：小麦的需求弹性小，增产的新技术使小麦供应增大，均衡价格降低，麦农更贫穷例2：OPEC减产以提高价格，短期内石油弹性小，价格高，长期上其他国家加大开发石油力度、消费者改用节能品，供应增加需求减少，价格回落例3：毒品禁令使毒品供应减少，但由于需求弹性小，用于毒品的总金额增大，导致更多犯罪，而毒品教育使毒品需求降低，均衡价格和数量均降低。
Chapter 5Elasticity and its applicationSolutions to text problemsprice elasticity of demand. Explain the relationship between total QZ Definerevenue and the price elasticity of demand. (page 92)The price elasticity of demand is a measure of how much the quantity demanded of a good responds to a change in the price of that good, calculated as the percentage change in quantity demanded divided by the percentage change in price.The relationship between total revenue and the price elasticity of demand is: (1) when a demand curve is inelastic (a price elasticity less than 1), a price increase raises total revenue, and a price decrease reduces total revenue; (2) when a demand curve is elastic (a price elasticity greater than 1), a price increase reduces total revenue, and a price decrease raises total revenue; and (3) when a demand curve is unit elastic (a price elasticity equal to 1), a change in price does not affect total revenue.price elasticity of supply. Explain why the price elasticity of supply QZ Definemight be different in the long run than in the short run. (page 94)The price elasticity of supply is a measure of how much the quantity supplied of a good responds to a change in the price of that good, calculated as the percentage change in quantity supplied divided by the percentage change in price.The price elasticity of supply might be different in the long run than in the short run because over short periods of time, firms cannot easily change the size of their factories to make more or less of a good. Thus, in the short run, the quantity supplied is not very responsive to the price. However, over longer periods, firms can build new factories or close old ones, or they can enter or exit a market. So, in the long run, the quantity supplied can respond substantially to the price.QZ How might a drought that destroys half of all farm crops be good for farmers? If such a drought is good for farmers, why don’t farmers destroy their own crops in the absence of a drought? (page 100)A drought that destroys half of all farm crops could be good for farmers if the demand for the crops is inelastic. The shift to the left of the supply curve leads to a price increase that raises total revenue because the price elasticity is less than one.Even though a drought could be good for farmers, they wouldn’t destroy their crops in the absence of a drought because no one farmer would have an incentive to destroy her crops, since she takes the market price as given. Only if all farmers destroyed their crops together, for example through a government program, would this plan work to make farmers better off.Questions for review (page 101)1The price elasticity of demand measures how much the quantity demanded responds to a change in price. The income elasticity of demand measures how much the quantity demanded changes as consumer income changes.2The determinants of the price elasticity of demand include whether the good is a necessity or a luxury, how available close substitutes are, how broadly defined the market is, and the time horizon.Luxury goods have greater price elasticity than necessities, goods with close substitutes have greater elasticity, goods in more narrowly defined markets have greater elasticity, and goods have greater elasticity the longer the time horizon.3Elasticity greater than 1 means demand is elastic. When the elasticity is greater than 1, the percentage change in quantity demanded exceeds the percentage change in price. When the elasticity60 Principles of Economics, Third edition, Instructor’s Manualequals 0, demand is perfectly inelastic. There is no change in quantity demanded when there is a change in price.4Figure 5.1 presents a supply-and-demand diagram, showing equilibrium price, equilibrium quantity, total spending by consumers and the total revenue received by producers. Total spending byconsumers equals the equilibrium price times the equilibrium quantity. Total revenue received by producers also equals the equilibrium price times the equilibrium quantity. These are shown by the area of the rectangle in Figure 5.1.Figure 5.15If demand is elastic, an increase in price reduces total revenue. With elastic demand, the quantity demanded falls by a greater percentage than the percentage increase in price. As a result, total revenue declines.6 A good with an income elasticity less than 0 is called an inferior good because as income rises, thequantity demanded declines.Chapter 5: Elasticity and its application 61 7The price elasticity of supply is calculated as the percentage change in quantity supplied divided by percentage change in price.Price elasticity of supply =% change in quantity supplied % change in priceIt measures how much the quantity supplied responds to changes in the price.8The price elasticity of supply of Picasso paintings is zero, since no matter how high price rises, no more can ever be produced.9The price elasticity of supply is usually larger in the long run than it is in the short run. Over short periods of time, firms cannot easily change the size of their factories to make more or less of a good, so the quantity supplied is not very responsive to price. Over longer periods, firms can build new factories or close old ones, so the quantity supplied is more responsive to price.10OPEC was unable to maintain a high price through the 1980s because the elasticity of supply and demand were more elastic in the long run. When the price of oil rose, producers of oil outside of OPEC increased oil exploration and built new extraction capacity. Consumers responded withgreater conservation efforts. As a result, supply increased and demand fell, leading to a lower price for oil in the long run.Problems and applications (page 102)1 a Mystery novels have more elastic demand than required textbooks, because mystery novels haveclose substitutes and are more of a luxury good, while required textbooks are more of a necessity with no close substitutes. If the price of mystery novels were to rise, readers could substituteother types of novels, or buy fewer novels altogether. But if the price of required textbooks were to rise, students would have little choice but to pay the higher price. Thus the quantity demanded of required textbooks is less responsive to price than the quantity demanded of mystery novels.b Beethoven recordings have more elastic demand than classical music recordings in general.Beethoven recordings are a narrower market than classical music recordings, so it is easy to find close substitutes for them. If the price of Beethoven recordings were to rise, people couldsubstitute other classical recordings, like Mozart. But if the price of all classical recordings were to rise, substitution would be more difficult. A transition from classical music to hip-hop, forexample, is less likely. Thus the quantity demanded of classical recordings is less responsive to price than the quantity demanded of Beethoven recordings.c Heating oil during the next 5 years has more elastic demand than heating oil during the next 6months. Goods have a more elastic demand over longer time horizons. If the price of heating oil were to rise temporarily, consumers couldn’t switch to other sources of fuel without greatexpense. But if the price of heating oil were to be high for a long time, people would gradually switch to gas or electric heat. As a result, the quantity demanded of heating oil during the next 6 months is less responsive to price than the quantity demanded of heating oil during the next 5years.d Lemonade has more elastic demand than water. Lemonade is a luxury with close substitutes,while water is a necessity with no close substitutes. If the price of water were to rise, consumers have little choice but to pay the higher price. But if the price of lemonade were to rise,consumers could easily switch to other soft drinks. So the quantity demanded of lemonade ismore responsive to price than the quantity demanded of water.2 a(i) For business travellers, the price elasticity of demand when the price of tickets risesfrom $200 to $250 is [(2,000 – 1,900)/1,950]/[(250 – 200)/225] = 3/13 = 0.23.(ii) For holiday-makers, the price elasticity of demand when the price of tickets risesfrom $200 to $250 is [(800 – 600)/700] / [(250 – 200)/225] = 9/7 = 1.29.b The price elasticity of demand for holiday-makers is higher than the elasticity for businesstravellers because holiday-makers can more easily choose a different mode of transportation like driving or taking the train. Business travellers are less likely to do so since time is moreimportant to them and their schedules are less adaptable.62 Principles of Economics, Third edition, Instructor’s Manual3 a(i) If your income is $10,000, your price elasticity of demand as the price of compactdiscs rises from $8 to $10 is [(40 – 32)/36] / [(10 – 8)/9] = 1(ii) If your income is $12,000, the elasticity is [(50 – 45)/47.5] / [(10 – 8)/9] = 9/19 =0.47b(i) If the price is $12, your income elasticity of demand as your income increases from $10,000 to $12,000 is [(30 – 24)/27] / [(12,000 – 10,000)/11,000] = 11/9 = 1.22.(ii) If the price is $16, your income elasticity of demand as your income increases from $10,000 to $12,000 is [(12 – 8)/10] / [(12,000 – 10,000)/11,000] = 11/5 = 2.2.4 a If Emily always spends one-third of her income on clothing, then her income elasticityof demand is one, since maintaining her clothing expenditures as a constant fraction ofher income means the percentage change in her quantity of clothing must equal herpercentage change in income. For example, suppose the price of clothing is $30, herincome is $9,000, and she purchases 100 clothing items. If her income rose 10 percentto $9,900, she’d spend a total of $3,300 on clothing, which is 110 clothing items, a 10percent increase.b Emily’s price elasticity of clothing demand is also one, since every percentage point increase inthe price of clothing would lead her to reduce her quantity purchased by the same percentage.Again, suppose the price of clothing is $30, her income is $9,000, and she purchases 100clothing items. If the price of clothing rose 1 percent to $30.30, she would purchase 99 clothing items, a 1 percent reduction. Note this part of the problem can be confusing to students if theyhave an example with a larger percentage change and they use the point elasticity calculationmethod. This example can be used to further illustrate the usefulness of the midpoint method for any size change.c Since Emily spends a smaller proportion of her income on clothing, then for any given price, herquantity demanded will be lower. Thus her demand curve has shifted to the left. But becauseshe’ll again spend a constant fraction of her income on clothing, her income and price elasticities of demand remain one.5 a With a 4.3 percent decline in quantity following a 20 percent increase in price, theprice elasticity of demand is only 4.3/20 = 0.215, which is fairly inelastic.b With inelastic demand, the revenue rises when the fare rises.c The elasticity estimate might be unreliable because it’s only the first month after the fareincrease. As time goes by, people may switch to other means of transportation in response to the price increase. So the elasticity may be larger in the long run than it is in the short run.6Tom’s price elasticity of demand is zero, since he wants the same quantity regardless of the price.Jerry’s price elasticity of demand is one, since he spends the same amount on gas, no matter what the price, which means his percentage change in quantity is equal to the percentage change in price.7To explain the observation that spending on restaurant meals declines more during economic downturns than does spending on food to be eaten at home, economists look at the income elasticity of demand. In economic downturns, people have lower income. To explain the observation, the income elasticity of restaurant meals must be larger than the income elasticity of spending on food to be eaten at home.8 a With a price elasticity of demand of 0.4, reducing the quantity demanded of cigarettes by 20percent requires a 50 percent increase in price, since 20/50 = 0.4. With the price of a pack ofcigarettes currently at $8, this would require an increase in the price to $13.33 a pack using the midpoint method (note that ($13.33 – $8)/$10.67 = 0.50).b The policy will have a larger effect five years from now than it does one year from now. Theelasticity is larger in the long run, since it may take some time for people to reduce theircigarette usage. The habit of smoking is hard to break in the short run.c Since teenagers don’t have as much income as adults, they are likely to have a higher priceelasticity of demand.9You’d expect the price elasticity of demand to be higher in the market for vanilla ice cream than for all ice cream because vanilla ice cream is a narrower category and other flavours of ice cream are almost perfect substitutes for vanilla.Chapter 5: Elasticity and its application 63 You’d expect the price elasticity of supply to be larger for vanilla ice cream than for all ice cream. A producer of vanilla ice cream could easily adjust the quantity of vanilla ice cream and produce other types of ice cream. But a producer of ice cream would have a more difficult time adjusting the overall quantity of ice cream they produced.10 a As Figure 5.2 shows, in both markets, the increase in supply reduces the equilibrium price andincreases the equilibrium quantity.b In the market for pharmaceutical drugs, with inelastic demand, the increase in supply leads to arelatively large decline in the price and not much of an increase in quantity. This marketexperiences a larger change in price.Figure 5.2c In the market for computers, with elastic demand, the increase in supply leads to a relativelylarge increase in quantity and not much of a decline in price. This market experiences a largerchange in quantity.d In the market for pharmaceutical drugs, since demand is inelastic, the percentage increase inquantity will be less than the percentage decrease in price, so total consumer spending willdecline. In contrast, since demand is elastic in the market for computers, the percentage increase in quantity will be greater than the percentage decrease in price, so total consumer spending will increase.11 a As Figure 5.3 shows, in both markets, the increase in demand increases both the equilibriumprice and the equilibrium quantity.b In the market for beachfront resorts, with inelastic supply, the increase in demand leads to arelatively large increase in the price and not much of an increase in quantity. This marketexperiences a larger change in price.c In the market for cars, with elastic supply, the increase in demand leads to a relatively largeincrease in quantity and not much of an increase in price. This market experiences a largerchange in quantity.d In both markets, total consumer spending rises, since both equilibrium price and equilibriumquantity rise.64 Principles of Economics, Third edition, Instructor’s Manual Figure 5.3Quantity of cars 12 a Vineyard owners whose vines weren’t destroyed benefited because the destruction of some ofthe vines reduced the supply, causing the equilibrium price to rise.b To tell whether vineyard owners as a group were hurt or helped by the floods, you’d need toknow the price elasticity of demand. It could be that the additional income earned by vineyard owners whose vines weren’t destroyed rose more because of the higher prices than the lossesmade by vineyard owners whose vines were destroyed, if demand is inelastic.13 A worldwide drought could increase the total revenue of farmers if the price elasticity of demand forgrain is inelastic. The drought reduces the supply of grain, but if demand is inelastic, the reduction of supply causes a large increase in price. Total farm revenue would rise as a result. If there’s only a drought in Queensland, Queensland’s production isn’t a large enough proportion of the total farm product to have much impact on the price. As a result, price is basically unchanged, while the output of Queensland farmers declines, thus reducing their income.14 When productivity increases for all farmland at a point in time, the increased productivity leads to arise in farmland prices, since more output can be produced on a given amount of land. But prior to the technological improvements, the productivity of farmland depended mainly on the prevailing weather conditions. There was little opportunity to substitute land with worse weather conditions for land with better weather conditions. As technology improved over time, it became much easier to substitute one type of land for another. So the price elasticity of supply for farmland increased over time, since now land with bad weather is a better substitute for land with good weather. Theincreased supply of land reduced farmland prices. As a result, productivity and farmland prices are negatively related over time.15 Not necessarily. If demand for luxury cars is price elastic, then raising the price of luxury cars byincreasing the tax will decrease the total revenue from luxury cars. It is likely that demand for luxury cars is elastic as they are more of a luxury than a necessity. P r i c e o f c a r s。
第五章弹性及其应用复习题1 •给需求价格弹性和需求收入弹性下定义。
答：需求价格弹性，是指一种物品需求量对其价格变动反应程度的衡量；需求收入弹性，是指一种物品需求量对消费者收入变动反应程度的衡量。
2 •列出并解释本章中所谈论的决定需求价格弹性的四个因素。
答：需求的价格弹性取决于许多形成个人欲望的经济、社会和心理因素。
通常，需求价格弹性主要由以下几个因素决定：（1）相似替代品的可获得性。
有相似替代品的物品往往富有需求弹性，因为消费者从这种物品转向其他物品较为容易。
（2）必需品与奢侈品。
必需品倾向于需求缺乏弹性，奢侈品倾向于需求富有弹性。
（3）市场的定义。
范围小的市场的需求弹性往大于范围大的市场，因为范围小的市场上的物品更容易找到相近的替代品。
（4）时间框架。
物品往往随着时间变长而需求更富有弹性，因为在长期中人们有充分的时间来改变自己的消费嗜好和消费结构。
4 •如果弹性大于1 ,需求是富有弹性还是缺乏弹性？如果弹性等于零，需求是完全有弹性还是完全无弹性？答：弹性大于1 ,需求富有弹性。
弹性等于零，需求完全无弹性。
5 •在一个供求图上标明均衡价格、均衡数量和生产者得到的总收益。
答：如图，供给与需求曲线的交点是均衡点，均衡点所对应的价格P是均衡价格，所对应的数量Q是均衡数量。
PQ,即阴影部分是生产者得到的总收益。
6 •如果需求是富有弹性的，价格上升会如何改变总收益？解释原因。
答：如果需求是富有弹性的，价格上升会使总收益减少。
因为需求富有弹性，价格上升引起需求量减少的如此之多，以至于大到抵消价格上涨所带来的收益，即需求量下降的比例大于价格上升的比例。
7 •如果一种物品需求收入弹性小于零，我们把这种物品称为什么？答：需求收入弹性小于零的物品，我们称为低档物品。
8•如何计算供给的价格弹性？供给价格弹性衡量什么？答：供给价格弹性=供给量变动的百分比/价格变动百分比。
它是衡量供给量对其价格变动的反应程度。
9 .毕加索油画的供给价格弹性是多大？答：毕加索油画的供给价格弹性为零。
