曼昆宏观经济学练习题及答案

Homework3(suggestedsolution)Duedate:Dec151.Supposethatthefollowingequationsdescribeaneconomy(C,I,G,T,andYaremeasuredinbillionsofdollarsandrismeasuredinpercent;forexample,r=10meansr=10percent):C=170+0.6(Y-T)T=200I=100-4rG=350(M/P)d=L=0.75Y−6rMs/P=M/P=735.a.GraphtheISandLMcurveandshowmetheslopesandintercepts.slopeofIScurve1/10;slopeofLMcurve1/8b.CalculatetheequilibriumlevelsofrealoutputY,theinterestrater,plannedinvestmentI,andconsumptionC.r15(percent);Y1,100;I40;C710c.AttheequilibriumlevelofrealoutputY,calculatethevalueofthegovernmentbudgetsurplus.150d.SupposethatGincreasesby36to386.DerivethenewISandLMequationsandplotanddrawthesecurvesonthegraphyoudrewforParta.TheLMequationremainsunchanged.ThenewISequationisY1,34010r.e.WhatisthehorizontalshiftintheIScurveand/ortheLMcurveinPartd(i.e.,ifrremainsconstant,byhowmuchdoesYincreaseoneachcurve)?TheshiftintheIScurveisequalto90.TheLMcurvedoesnotshift.f.RefertotheISandLMequationsyouderivedinPartd.WithYontheleft-handsideoftheequations,calculatethenewequilibriumlevelsofrealoutputY,theinterestrater,plannedinvestmentI,andconsumptionC.Y1,140;r20;I20;C734g.InsteadofincreasingG,supposethattheFedsoughttoachievetheequilibriumlevelofrealoutputYinParththroughexpansionarymonetarypolicyalone.ByhowmuchwouldtheFedhavetoincreasethemoneysupply?54h.ComparetheequilibriumlevelsofconsumptionC,governmentspendingG,andplannedinvestmentIinPartsfandg.Basedonthiscomparison,whymightsomeeconomistspreferexpansionaryfiscalpolicywhileotherspreferexpansionarymonetarypolicy?GovernmentpurchasesarehigherinPartf.SincetaxesandoutputarethesameasPartsfandg,consumptionisalsothesame.SincetheinterestrateislowerinPartg,investmentishigher.AdvocatesofexpansionaryfiscalpolicymayarguethattheUnitedStatesisbadlyinneedofpublicspendinginareaslikeeducation,defense,andinfrastructure.Advocatesofexpansionarymonetarypolicy,ontheotherhand,wouldtoutitseffectoninvestment,whichmightspureconomicgrowthasthecapitalstockgrows.2.a.In2009,PresidentObamaincreasedgovernmentspendingandcutnettaxes.DrawtheappropriategraphstoindicatewhatwouldhappentotheIS,LM,aggregatedemand,andshort-runaggregatesupplycurves,andindicateanyshort-runchangesintheequilibriumlevelsofr,I,C,G,Y,andPiftheFedhadnotchangedanyofitspolicies.AnincreaseinGandcutinnettaxesTshifttheISandADcurvestotheright(orISandADcurvesshiftupward).TheSRASandLMcurvesdonotshiftintheshortrun.TheequilibriumlevelsofY,r,andCallrise.TheequilibriumlevelofIfalls,andGandPdonotchangeintheshortrun(giventhehorizontalSRAScurveofChapter9)b.Duringthisperiod,theFedactuallypursuedexpansionarymonetarypolicyandkeptinterestratesnearlyconstant.RedrawyourdiagramsfromPartaandindicatewhatactuallyhappenedtotheIScurve,LMcurve,aggregatedemandcurve,short-runaggregatesupplycurve,andthelevelsofr,I,C,G,Y,andP.HowdotheycomparewiththelevelsinParta?TheFederalReserveincreasedthemoneysupplyatthesametimeasgovernmentspendingroseandtaxesfell.Consequently,boththeISandLMcurvesshiftedtotheright.ThisshiftedtheADcurveevenfarthertotheright.ThelevelsofYandCrisebymoreinPartbthaninParta.Theremainingvariables,r,I,G,andPremainconstant.3.TheFedisconsideringtwoalternativemonetarypolicies:holdingthemoneysupplyconstantandlettingtheinterestrateadjust,or•adjustingthemoneysupplytoholdtheinterestrateconstant.IntheIS–LMmodel,whichpolicywillbetterstabilizeoutputunderthefollowingconditions?a.Allshockstotheeconomyarisefromexogenouschangesinthedemandforgoodsandservices.Figure11–25(A)showswhattheIS–LMmodellookslikeforthecaseinwhichtheFedholdsthemoneysupplyconstant.Figure11–25(B)showswhatthemodellookslikeiftheFedadjuststhemoneysupplytoholdtheinterestrateconstant;thispolicymakestheeffectiveLMcurvehorizontal.Ifallshockstotheeconomyarisefromexogenouschangesinthedemandforgoodsandservices,thismeansthatallshocksaretotheIScurve.SupposeashockcausestheIScurvetoshiftfromIS1toIS2.Figures11–26(A)and(B)showwhateffectthishasonoutputunderthetwopolicies.ItisclearthatoutputfluctuateslessiftheFedfollowsapolicyofkeepingthemoneysupplyconstant.Thus,ifallshocksaretotheIScurve,thentheFedshouldfollowapolicyofkeepingthemoneysupplyconstant.b.Allshockstotheeconomyarisefromexogenouschangesinthedemandformoney.Ifallshocksintheeconomyarisefromexogenouschangesinthedemandformoney,thismeansthatallshocksaretotheLMcurve.IftheFedfollowsapolicyofadjustingthemoneysupplytokeeptheinterestrateconstant,thentheLMcurvedoesnotshiftinresponsetotheseshocks—theFedimmediatelyadjuststhemoneysupplytokeepthemoneymarketinequilibrium.Figures11–27(A)and(B)showtheeffectsofthetwopolicies.ItisclearthatoutputfluctuateslessiftheFedholdstheinterestrateconstant,asinFigure11–27(B).IftheFedholdstheinterestrateconstantandoffsetsshockstomoneydemandbychangingthemoneysupply,thenallvariabilityinoutputiseliminated.Thus,ifallshocksaretotheLMcurve,thentheFedshouldadjustthemoneysupplytoholdtheinterestrateconconstant,therebystabilizingoutput.