经济学原理第三版习题答案IV.docx

经济学原理第三版习题答案IV.docx

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经济学原理第三版习题答案IV

SOLUTIONSTOTEXTPROBLEMS:

QuickQuizzes

1.FarmerMcDonald’sopportunitycostis$300,consistingof10hoursoflessonsat$20anhourthathecouldhavebeenearningplus$100inseeds.Hisaccountantwouldnotcountthelostbanjo-lessonmoney,onlytheseeds,worth$100.IfMcDonaldearns$200fromsellingthecrops,thenMcDonaldearnsa$100accountingprofit（$200salesminus$100costofseeds）butmakesaneconomiclossof$100（$200salesminus$300opportunitycost）.

2.FarmerJones’sproductionfunctionisshowninFigure1andhistotal-costcurveisshowninFigure2.Theproductionfunctionisconcavebecauseofdiminishingmarginalproduct.Asthenumberofbagsofseedsincreases,themarginalproductdeclines,andtheproductionfunctionbecomesflatter.Thetotal-costcurveisconvex,asthecurvegetssteeperastheamountofproductionincreases.Thatisalsoafeaturethatarisesbecauseofdiminishingmarginalproduct,sinceeachadditionalbagofseedshaslowermarginalproductandthusthecostofproducingadditionalbushelsofwheatgoesup.

Figure1Figure2

3.Theaveragetotalcostofproducing5carsis$250,000/5=$50,000.Sincetotalcostrosefrom$225,000to$250,000whenoutputincreasedfrom4to5,themarginalcostofthefifthcaris$25,000.

Themarginal-costcurveandtheaverage-total-costcurveforatypicalfirmareshowninFigure3.Theycrossattheefficientscalebecauseatlowlevelsofoutput,marginalcostisbelowaveragetotalcost,soaveragetotalcostisfalling.Butafterthetwocurvescross,marginalcostrisesaboveaveragetotalcost,andaveragetotalcoststartstorise.Sothepointofintersectionmustbetheminimumofaveragetotalcost.

Figure3

4.Thelong-runaveragetotalcostofproducing9planesis$9million/9=$1million.Thelong-runaveragetotalcostofproducing10planesis$9.5million/10=$0.95million.Sincethelong-runaveragetotalcostdeclinesasthenumberofplanesincreases,Boeingexhibitseconomiesofscale.

QuestionsforReview

1.Therelationshipbetweenafirm'stotalrevenue,profit,andtotalcostisprofitequalstotalrevenueminustotalcosts.

2.Anaccountantwouldnotcounttheowner’sopportunitycostofalternativeemploymentasanaccountingcost.AnexampleisgiveninthetextinwhichHelenrunsacookiebusiness,butshecouldinsteadworkasacomputerprogrammer.Becauseshe'sworkinginhercookiefactory,shegivesuptheopportunitytoearn$100perhourasacomputerprogrammer.Theaccountantignoresthisopportunitycostbecausenomoneyflowoccurs.ButthecostisrelevanttoHelen'sdecisiontorunthecookiefactory.

3.Marginalproductistheincreaseinoutputthatarisesfromanadditionalunitofinput.Diminishingmarginalproductmeansthatthemarginalproductofaninputdeclinesasthequantityoftheinputincreases.

4.Figure4showsaproductionfunctionthatexhibitsdiminishingmarginalproductoflabor.Figure5showstheassociatedtotal-costcurve.Theproductionfunctionisconcavebecauseofdiminishingmarginalproduct,whilethetotal-costcurveisconvexforthesamereason.

Figure4Figure5

5.Totalcostconsistsofthecostsofallinputsneededtoproduceagivenquantityofoutput.Itincludesfixedcostsandvariablecosts.Averagetotalcostisthecostofatypicalunitofoutputandisequaltototalcostdividedbythequantityproduced.Marginalcostisthecostofproducinganadditionalunitofoutputandisequaltothechangeintotalcostdividedbythechangeinquantity.Anadditionalrelationbetweenaveragetotalcostandmarginalcostisthatwhenevermarginalcostislessthanaveragetotalcost,averagetotalcostisdeclining;whenevermarginalcostisgreaterthanaveragetotalcost,averagetotalcostisrising.

6.Figure6showsthemarginal-costcurveandtheaverage-total-costcurveforatypicalfirm.Ithasthreemainfeatures:

（1）marginalcostisrising;

（2）averagetotalcostisU-shaped;and（3）whenevermarginalcostislessthanaveragetotalcost,averagetotalcostisdeclining;whenevermarginalcostisgreaterthanaveragetotalcost,averagetotalcostisrising.Marginalcostisrisingforoutputgreaterthanacertainquantitybecauseintheshortrunthefirmmusthireadditionallabortoproducemoreoutputwithoutbeingabletobuyadditionalequipment.TheaveragetotalcostcurveisU-shapedbecausethefirminitiallyisabletospreadoutfixedcostsoveradditionalunits,butasquantityincreases,itcostsmoretoincreasequantityfurtherbecausesomeimportantinputislimited.Marginalcostandaveragetotalcosthavetherelationshiptheydobecausemarginalcostpullsaveragetotalcostinthesamedirection.Themarginalcostandaveragetotalcostcurvesintersectattheminimumofaveragetotalcost;thatquantityistheefficientscale.

Figure6

7.Inthelongrun,afirmcanadjustthefactorsofproductionthatarefixedintheshortrun;forexample,itcanincreasethesizeofitsfactory.Asaresult,thelong-runaverage-total-costcurvehasamuchflatterU-shapethantheshort-runaverage-total-costcurve.Inaddition,thelong-runcurveliesalongthelowerenvelopeoftheshort-runcurves.

8.Economiesofscaleexistwhenlong-runaveragetotalcostfallsasthequantityofoutputincreases,whichoccursbecauseofspecializationamongworkers.Diseconomiesofscaleexistwhenlong-runaveragetotalcostrisesasthequantityofoutputincreases,whichoccursbecauseofcoordinationproblemsinherentinalargeorganization.

ProblemsandApplications

1.a.opportunitycost;b.averagetotalcost;c.fixedcost;d.variablecost;e.totalcost;

f.marginalcost.

2.a.Theopportunitycostofsomethingiswhatmustbeforgonetoacquireit.

b.Theopportunitycostofrunningthehardwarestoreis$550,000,consistingof$500,000torentthestoreandbuythestockanda$50,000opportunitycost,sinceyourauntwouldquitherjobasanaccountanttorunthestore.Sincethetotalopportunitycostof$550,000exceedsrevenueof$510,000,yourauntshouldnotopenthestore,asherprofitwouldbenegative−shewouldlosemoney.

3.a.Sinceyouwouldhavetopayforroomandboardwhetheryouwenttocollegeornot,thatportionofyourcollegepaymentisnotanopportunitycost.

b.Theexplicitopportunitycostisthecostoftuitionandbooks.

c.Animplicitopportunitycostisthecostofyourtime.Youcouldworkatajobforpayratherthanattendcollege.Thewagesyougiveuprepresentanopportunitycostofattendingcollege.

4.a.Thefollowingtableshowsthemarginalproductofeachhourspentfishing:

Hours

Fish

FixedCost

VariableCost

TotalCost

MarginalProduct

0

0

$10

$0

$10

---

1

10

10

5

15

10

2

18

10

10

20

8

3

24

10

15

25

6

4

28

10

20

30

4

5

30

10

25

25

2

b.Figure7graphsthefisherman'sproductionfunction.Theproductionfunctionbecomesflatterasthenumberofhoursspentfishingincreases,illustratingdiminishingmarginalproduct.

Figure7

c.Thetableshowsthefixedcost,variablecost,andtotalcostoffishing.Figure8showsthefisherman'stotal-costcurve.Itslopesupbecausecatchingadditionalfishtakesadditionaltime.Thecurveisconvexbecausetherearediminishingreturnstofishingtime−eachadditionalhourspentfishingyieldsfeweradditionalfish.

Figure8

5.Hereisthetableofcosts:

Workers

Output

MarginalProduct

TotalCost

AverageTotalCost

MarginalCost

0

0

---

$200

---

---

1

20

20

300

$15.00

$5.00

2

50

30

400

8.00

3.33

3

90

40

500

5.56

2.50

4

120

30

600

5.00

3.33

5

140

20

700

5.00

5.00

6

150

10

800

5.33

10.00

7

155

5

900

5.81

20.00

a.Seetableformarginalproduct.Marginalproductrisesatfirst,thendeclinesbecauseofdiminishingmarginalproduct.

b.Seetablefortotalcost.

c.Seetableforaveragetotalcost.AveragetotalcostisU-shaped.Whenquantityislow,averagetotalcostdeclinesasquantityrises;whenquantityishigh,averagetotalcostrisesasquantityrises.

d.Seetableformarginalcost.MarginalcostisalsoU-shaped,butrisessteeplyasoutputincreases.Thisisduetodiminishingmarginalproduct.

e.Whenmarginalproductisrising,marginalcostisfalling,andviceversa.

f.Whenmarginalcostislessthanaveragetotalcost,averagetotalcostisfalling;thecostofthelastunitproducedpullstheaveragedown.Whenmarginalcostisgreaterthanaveragetotalcost,averagetotalcostisrising;thecostofthelastunitproducedpushestheaverageup.

6.Fixedcostsincludethecostofowningorrentingacartodeliverthebagelsandthecostofadvertising;theyarefixedcostsbecausetheydonotvarywithoutput.Variablecostsincludethecostofthebagelsandgasforthecar,sincethosecostswillincreaseasoutputincreases.

7.a.Thefixedcostis$300,sincefixedcostequalstotalcostminusvariablecost.

b.

Quantity

TotalCost

VariableCost

MarginalCost（usingtotalcost）

MarginalCost

（usingvariablecost）

0

$300

$0

---

---

1

350

50

$50

$50

2

390

90

40

40

3

420

120

30

30

4

450

150

30

30

5

490

190

40

40

6

540

240

50

50

Marginalcostequalsthechangeintotalcostorthechangeinvariablecost.Thatisbecausetotalcostequalsvariablecostplusfixedcostandfixedcostdoesnotchangeasthequantitychanges.Soasquantityincreases,theincreaseintotalcostequalstheincreaseinvariablecostandbothareequaltomarginalcost.

8.a.Thefixedcostofsettingupthelemonadestandis$200.Thevariablecostpercupis50cents.

Figure9

b.Thefollowingtableshowstotalcost,averagetotal