数据模型与决策运筹学课后习题和案例答案008Word下载.docx
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（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.
8.4-1Thethreeestimatesarethemostlikelyestimate,optimisticestimate,andpessimisticestimate.
8.4-2Theoptimisticandpessimisticestimatesaremeanttolieattheextremesofwhatispossible,whereasthemostlikelyestimateprovidesthehighestpointoftheprobabilitydistribution.
8.4-3Itisassumedthatthemeancriticalpathwillturnouttobethelongestpaththroughtheprojectnetwork.
8.4-4Itisassumedthatthedurationsoftheactivitiesonthemeancriticalpatharestatisticallyindependent.
8.4-5μp=sumofthemeansofthedurationsfortheactivitiesonthemeancriticalpath.
8.4-6σp2=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.
8.6-6APERT/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.
8.7-7Itencourageseffectiveinteractionbetweentheprojectmanagerandsubordinatesthatleadstosettingmutualgoalsfortheproject.
8.7-8Newimprovementsandextensionsarestillbeingdevelopedbuthavenotbeenincorporatedmuchintopracticeyet.
Problems
8.1a）
b）StartACFinishLength=4weeks
StartADEFinishLength=7weeks
StartBCFinishLength=5weeks
StartBDEFinishLength=8weeks*criticalpath
c）
Activity
ES
EF
LS
LF
Slack
CriticalPath
Start
Yes
A
2
1
3
No
B
C
5
6
8
D
E
Finish
CriticalPath:
StartBDEFinish
d）No,thiswillnotshortenthelengthoftheprojectbecausetheactivityisnotonthecriticalpath.
8.2a）
b）StartADFinishLength=4weeks
StartAEFinishLength=5weeks
StartAFKFinisLength=8weeks*criticalpath
StartAGHIJFinishLength=8weeks*criticalpath
StartBDFinishLength=3weeks
StartBCEFinishLength=6weeks
StartBCHIJFinishLength=8weeks*criticalpath
StartBCKFinishLength=7weeks
4
F
G
H
I
J
K
CriticalPaths:
StartAFKFinish
StartAGHIJFinish
StartBCHIJFinish
d）No,thiswillnotshortenthelengthoftheprojectbecauseAisnotonallofthecriticalpaths.
8.3a）
b,c,&
d）
7
10
11
15
17
18
16
19
L
20
M
23
24
N
StartABCFHIJLNFinish
StartABDGIJLNFinish
8.4a）
b）StartABJLFinishLength=75minutes*criticalpath
StartCDJLFinishLength=45minutes
StartEFJLFinishLength=72minutes
StartGHIJLFinishLength=67minutes
StartKLFinishLength=45minutes
c,d&
e）
30
35
32
25
33
27
45
75
CriticalPath:
StartABJLFinish
f）Dinnerwillbedelayed3minutesbecauseofthephonecall.Ifthefoodprocessorisusedthendinnerwillnotbedelayedbecausetherewas3minutesofslackand5minutesofcuttingtimesavedandthecallonlyused6minutesofthe8total.
8.5a）StartADHMFinishLength=19weeks
StartBEJMFinishLength=20weeks*criticalpath
StartCFKNFinishLength=16weeks
StartAIMFinishLength=17weeks
StartCGLNFinishLength=20weeks*criticalpath
b）
12
13
14
9
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