经济学原理第三版习题答案.docx

经济学原理第三版习题答案SOLUTIONSTOTEXTPROBLEMS:QuickQuizzes1.Whenacompetitivefirmdoublestheamountitsells,thepriceremainsthesame,soitstotalrevenuedoubles.2.Thepricefacedbyaprofit-maximizingfirmisequaltoitsmarginalcostbecauseifpricewereabovemarginalcost,thefirmcouldincreaseprofitsbyincreasingoutput,whileifpricewerebelowmarginalcost,thefirmcouldincreaseprofitsbydecreasingoutput.Aprofit-maximizingfirmdecidestoshutdownintheshortrunwhenpriceislessthanaveragevariablecost.Inthelongrun,afirmwillexitamarketwhenpriceislessthanaveragetotalcost.3.Inthelongrun,withfreeentryandexit,thepriceinthemarketisequaltobothafirmsmarginalcostanditsaveragetotalcost,asFigure1shows.Thefirmchoosesitsquantitysothatmarginalcostequalsprice;doingsoensuresthatthefirmismaximizingitsprofit.Inthelongrun,entryintoandexitfromtheindustrydrivethepriceofthegoodtotheminimumpointontheaverage-total-costcurve.Figure1QuestionsforReview1.Acompetitivefirmisafirminamarketinwhich:(1)therearemanybuyersandmanysellersinthemarket;(2)thegoodsofferedbythevarioussellersarelargelythesame;and(3)usuallyfirmscanfreelyenterorexitthemarket.2.Figure2showsthecostcurvesforatypicalfirm.Foragivenprice(suchasP*),thelevelofoutputthatmaximizesprofitistheoutputwheremarginalcostequalsprice(Q*),aslongaspriceisgreaterthanaveragevariablecostatthatpoint(intheshortrun),orgreaterthanaveragetotalcost(inthelongrun).Figure23.Afirmwillshutdowntemporarilyiftherevenueitwouldgetfromproducingislessthanthevariablecostsofproduction.Thisoccursifpriceislessthanaveragevariablecost.4.Afirmwillexitamarketiftherevenueitwouldgetifitstayedinbusinessislessthanitstotalcost.Thisoccursifpriceislessthanaveragetotalcost.5.Afirm'spriceequalsmarginalcostinboththeshortrunandthelongrun.Inboththeshortrunandthelongrun,priceequalsmarginalrevenue.Thefirmshouldincreaseoutputaslongasmarginalrevenueexceedsmarginalcost,andreduceoutputifmarginalrevenueislessthanmarginalcost.Profitsaremaximizedwhenmarginalrevenueequalsmarginalcost.6.Thefirm'spriceequalstheminimumofaveragetotalcostonlyinthelongrun.Intheshortrun,pricemaybegreaterthanaveragetotalcost,inwhichcasethefirmismakingprofits,orpricemaybelessthanaveragetotalcost,inwhichcasethefirmismakinglosses.Butthesituationisdifferentinthelongrun.Iffirmsaremakingprofits,otherfirmswillentertheindustry,whichwilllowerthepriceofthegood.Iffirmsaremakinglosses,theywillexittheindustry,whichwillraisethepriceofthegood.Entryorexitcontinuesuntilfirmsaremakingneitherprofitsnorlosses.Atthatpoint,priceequalsaveragetotalcost.7.Marketsupplycurvesaretypicallymoreelasticinthelongrunthanintheshortrun.Inacompetitivemarket,sinceentryorexitoccursuntilpriceequalstheminimumofaveragetotalcost,thesupplycurveisperfectlyelasticinthelongrun.ProblemsandApplications1.Acompetitivemarketisoneinwhich:(1)therearemanybuyersandmanysellersinthemarket;(2)thegoodsofferedbythevarioussellersarelargelythesame;and(3)usuallyfirmscanfreelyenterorexitthemarket.Ofthesegoods,bottledwaterisprobablytheclosesttoacompetitivemarket.Tapwaterisanaturalmonopolybecausethere'sonlyoneseller.Colaandbeerarenotperfectlycompetitivebecauseeverybrandisslightlydifferent.2.Sinceanewcustomerisofferingtopay$300foronedose,marginalrevenuebetween200and201dosesis$300.Sowemustfindoutifmarginalcostisgreaterthanorlessthan$300.Todothis,calculatetotalcostfor200dosesand201doses,andcalculatetheincreaseintotalcost.