微观经济Lecture4.ppt

微观经济Lecture4.ppt

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2010PearsonEducationCanada2010PearsonEducationCanadaWhataretheeffectsofahighgaspriceonbuyingplans?

HowyourdemandisaffectedbyhigherpricesButhowbigaretheseeffects?

Whenthepriceofgasolinedoubles,byhowmuchdoesthequantityofSUVssolddecrease,andbyhowmuchdoesthequantityofsub-compactssoldincrease?

Whataboutgasolinepurchases?

Dowespendmoreongasordowefindsubstitutesandspendlessongas?

Elasticityisatoolthataddressesthesequestions.2010PearsonEducationCanadaElasticityisameasureofhowmuchbuyersandsellersrespondtochangesinmarketconditions.measureshowresponsiveQdorQsistochangesinprice,incomeorpricesofrelatedgoods.allowsustoanalyzesupplyanddemandwithgreaterprecision.2010PearsonEducationCanadaTHEELASTICITYOFDEMANDPriceelasticityofdemandisameasureofhowmuchthequantitydemandedofagoodrespondstoachangeinthepriceofthatgood.Priceelasticityofdemandisthepercentagechangeinquantitydemandedgivenapercentchangeintheprice.2010PearsonEducationCanadaPriceElasticityofDemandInFigure4.1（a）,anincreaseinsupplybringsAlargefallinpriceAsmallincreaseinthequantitydemanded2010PearsonEducationCanadaInFigure4.1（b）,anincreaseinsupplybringsAsmallfallinpriceAlargeincreaseinthequantitydemandedPriceElasticityofDemand2010PearsonEducationCanadaThecontrastbetweenthetwooutcomesinFigure4.1highlightstheneedforAmeasureoftheresponsivenessofthequantitydemandedtoapricechange.Thepriceelasticityofdemandisaunits-freemeasureoftheresponsivenessofthequantitydemandedofagoodtoachangeinitspricewhenallotherinfluencesonbuyersplansremainthesame.PriceElasticityofDemand2010PearsonEducationCanadaCalculatingElasticityThepriceelasticityofdemandiscalculatedbyusingtheformula:

PercentagechangeinquantitydemandedPercentagechangeinpricePriceElasticityofDemand2010PearsonEducationCanadaTocalculatethepriceelasticityofdemand:

Weexpressthechangeinpriceasapercentageoftheaveragepricetheaverageoftheinitialandnewprice,andweexpressthechangeinthequantitydemandedasapercentageoftheaveragequantitydemandedtheaverageoftheinitialandnewquantity.PriceElasticityofDemand2010PearsonEducationCanadaCalculatingElasticityIfwearegivenpercentagechangesinpriceandthecorrespondingchangesinQd,weusetheformulaEp=%rrinQd%rrinPForexample,Thepriceofmilkincreasesby2%andQddecreasesby.5%Ep=-.5/2=-.252010PearsonEducationCanadaAnotherformulaweuseisthemidpointformula.Themidpointformulaispreferablewhencalculatingthepriceelasticityofdemandbecauseitgivesthesameanswerregardlessofthedirectionofthechange.WeuseitwhenwearegiventwopricesandtheircorrespondingQdvalues.2010PearsonEducationCanadaThemidpointformulais:

Ep=（Q2Q1）/（Q2+Q1/2）（P2P1）/（P2+P1/2）Example:

Ifthepriceofanicecreamconeincreasesfrom$2.00to$2.20andtheamountyoubuyfallsfrom10to8cones,thenyourelasticityofdemandwouldbecalculatedas:

2010PearsonEducationCanadaP1=2.00P2=2.20Q1=10Q2=8Ep=（810）/（8+10）/2（2.20-2.00）/（2.20+2.00）/2=-2/9.20/2.10=-.22/.095=-2.322010PearsonEducationCanadaInbothexamples,wehaveanelasticitycoefficientthathasanegativesign.But,rememberthelawofdemand:

asPhh,Qdii.Thecoefficientwillalwaysbeanegativenumber.2010PearsonEducationCanadaSo,inourmilkexample,Ep=.25SinceEp1,thedemandforicecreamiselastic.Demandrespondsstronglytochangesinprice.2010PearsonEducationCanadaComputingthePriceElasticityofDemandDemandispriceelastic$54DemandQuantity100050Price2010PearsonEducationCanadaFigure4.2calculatesthepriceelasticityofdemandforpizza.Thepriceinitiallyis$20.50andthequantitydemandedis9pizzasanhour.PriceElasticityofDemand2010PearsonEducationCanadaThepricefallsto$19.50andthequantitydemandedincreasesto11pizzasanhour.Thepricefallsby$1andthequantitydemandedincreasesby2pizzasanhour.PriceElasticityofDemand2010PearsonEducationCanadaTheaveragepriceis$20andtheaveragequantitydemandedis10pizzasanhour.PriceElasticityofDemand2010PearsonEducationCanadaThepercentagechangeinquantitydemanded,%DQ,iscalculatedasDQ/Qave,whichis2/10=1/5.Thepercentagechangeinprice,%DP,iscalculatedasDP/Pave,whichis$1/$20=1/20.PriceElasticityofDemand2010PearsonEducationCanadaThepriceelasticityofdemandis%DQ/%DP=（1/5）/（1/20）=20/5=4.PriceElasticityofDemand2010PearsonEducationCanadaByusingtheaveragepriceandaveragequantity,wegetthesameelasticityvalueregardlessofwhetherthepricerisesorfalls.Theratiooftwoproportionatechangesisthesameastheratiooftwopercentagechanges.Themeasureisunitsfreebecauseitisaratiooftwopercentagechangesandthepercent