数据模型与决策(运筹学)课后习题和案例答案008

8-1CHAPTER8PERT/CPMMODELSFORPROJECTMANAGEMENTReviewQuestions8.1-1Thebidisfor$5.4millionwithapenaltyof$300,000ifthedeadlineof47weeksisnotmet.Inaddition,abonusof$150,000willbepaidiftheplantiscompletedwithin40weeks.8.1-2Hehasdecidedtofocusonmeetingthedeadlineof47weeks.8.1-3Animmediatepredecessorisanactivitythatmustbecompletedjustpriortostartingthegivenactivity.Giventheimmediatepredecessorsofanactivity,thisactivitythenbecomestheimmediatesuccessorofeachoftheseimmediatepredecessors.8.1-4(1)theactivitiesoftheproject;(2)theimmediatepredecessorsoftheactivities;and(3)theestimateddurationoftheactivities8.2-1(1)activityinformation;(2)precedencerelationships;and(3)timeinformation(duration)8.2-2InanAOAnetwork,eachactivityisrepresentedbyanarc,whileinanAONnetwork,eachactivityisrepresentedbyanode.AONnetworksarebeingusedhere.8.2-3ThebarsinaGanttchartshowthescheduledstartandfinishtimesforactivitiesinaproject.8.3-1(a)Apaththroughaprojectnetworkisoneoftheroutesfollowingthearrows(arcs)fromthestartnodetothefinishnode;(b)thelengthofapathisthesumoftheestimateddurationsoftheactivitiesonthepath;(c)thelongestpathiscalledthecriticalpath.8.3-2(1)Theactualdurationofeachactivitymustbethesameasitsestimatedduration;and(2)eachactivitymustbeginassoonasallitsimmediatepredecessorsarefinished.8.3-3Theearlieststarttimeofanactivityisequaltothelargestoftheearliestfinishtimesofitsimmediatepredecessors.8.3-4Aforwardpassistheprocessofstartingwiththeinitialactivitiesandworkingforwardintimetowardthefinalactivities.8.3-5Itisalastchanceschedulebecauseanythinglaterwilldelaythecompletionoftheproject.8.3-6Thelatestfinishtimeofanactivityisequaltothesmallestofthelateststarttimesofitsimmediatesuccessors.8.3-7Abackwardpassstartswiththefinalactivitiesandworksbackwardintimetowardtheinitialactivitiesinsteadofstartingwiththeinitialactivities.8.3-8Anydelayalongthecriticalpathwilldelayprojectcompletion.8.3-9(1)Identifythelongestpaththroughtheprojectnetwork;and(2)identifytheactivitieswithzeroslack—theyareonthecriticalpath.8-28.4-1Thethreeestimatesarethemostlikelyestimate,optimisticestimate,andpessimisticestimate.8.4-2Theoptimisticandpessimisticestimatesaremeanttolieattheextremesofwhatispossible,whereasthemostlikelyestimateprovidesthehighestpointoftheprobabilitydistribution.8.4-3Itisassumedthatthemeancriticalpathwillturnouttobethelongestpaththroughtheprojectnetwork.8.4-4Itisassumedthatthedurationsoftheactivitiesonthemeancriticalpatharestatisticallyindependent.8.4-5p=sumofthemeansofthedurationsfortheactivitiesonthemeancriticalpath.8.4-6p2=sumofthevariancesofthedurationsfortheactivitiesonthemeancriticalpath.8.4-7Itisassumedthattheformoftheprobabilitydistributionofprojectdurationisthenormaldistribution.8.4-8Itisusuallyhigherthanthetrueprobability.8.5-1Usingovertime,hiringadditionallabor,andusingspecialmaterialsorequipmentareallwaysofcrashinganactivity.8.5-2Thetwokeypointsarelabelednormalandcrash.Thenormalpointshowsthetimeandcostoftheactivitywhenitisperformedinthenormalway.Thecrashpointshowsthetimeandcostwhentheactivityisfullycrashed.8.5-3No,onlycrashingactivitiesonthecriticalpathwillreducethedurationoftheproject.8.5-4Crashcostsperweeksavedarebeingexamined.8.5-5Thedecisionstobemadearethestarttimeofeachactivity,thereductioninthedurationofeachactivityduetocrashing,andthefinishtimeoftheproject.8.5-6Anactivitycannotstartuntilitsimmediatepredecessorstartsandthencompletesitsduration.8.5-7Becauseofuncertainty,theplanforcrashingtheprojectonlyprovidesa50%chanceofactuallyfinishingwithin40weeks,sotheextracostoftheplanisnotjustified.8.6-1PERT/Costisasystematicproceduretohelpthemanagerplan,schedule,andcontrolprojectcosts.8.6-2Itbeginsbydevelopinganestimateofthecostofeachactivitywhenitisperformedintheplannedway.8.6-3Acommonassumptionisthatthecostsofperforminganactivityareincurredataconstantratethroughoutitsduration.8.6-4Aworkpackageisagroupofrelatedactivities.8.6-5PERT/Costusesearlieststarttimeandlateststarttimeschedulesasabasisfordevelopingcostschedules.8-38.6-6APERT/Costscheduleofcostsshowstheweeklyprojectcostandcumulativeprojectcostforeachtimeperiod.8.6-7APERT/Costreportshowsthebudgetedvalueoftheworkcompletedofeachactivityandthecostoverrunstodate.8.6-8Sincedeviationsfromtheplannedworkschedulemayoccur,aPERT/Costreportisneededtoevaluatethecostperformanceofindividualactivities.8.7-1Planning,scheduling,dealingwithuncertainty,time-costtrade-offs,andcontrollingcostsareaddressedbyPERT/CPM.8.7-2Computerimplementationhasallowedforapplicationtolargerprojects,fasterrevisionsinprojectplansandeffortlessupdatesandchangesinschedules.8.7-3Theaccuracyandreliabilityofend-pointestimatesarenotasgoodforpointsthatarenotattheextremesoftheprobabilitydistribution.8.7-4ThetechniqueofcomputersimulationtoapproximatetheprobabilitythattheprojectwillmeetitsdeadlineisanalternativeforimprovingonPERT/CPM.8.7-5ThePrecedenceDiagrammingMethodhasbeendevelopedasanextensionofPERT/CPMtodealwithoverlappingactivities.8.7-6PERT/CPMassumesthateachactivityhasavailablealltheresourcesneededtoperformtheactivityinanormalway.8.7-7It