7/25/2019 Review Questions Session 3
1/2
ReviewQuestionsSession3
QuickLubeInc.
QuickLubeInc.operatesafastlubeandoilchangegarage.Onatypicaldaycustomersarriveatthe
rateofthreeperhour,andlubejobsareperformedatanaveragerateofoneevery15minutes.The
mechanicsoperateasateamononecaratatime.
A. AssumingPoisson
arrivals
(CVA=1)
and
exponential
service
(CVS=1)
find
the
average
time
acarwaitsbeforeitislubed.
B.
AssumingPoissonarrivals(CVA=1)andexponentialservice(CVS=1)findtheaveragenumber
ofcarsinline.
Afterpurchasinganewmachinetheteamchangesitsoperatingprocedures.Withthisnewmachine
lubejobsarestillperformedatanaveragerateofoneevery15minutes.However,everylubejob
nowlastsexactly15minutes.
C. Whatwouldhappentotheaveragewaitingtime?
a)Itwoulddecrease.
b)Itwouldnotchange.
c)Itwouldincrease.
D. Whatwouldhappentotheaveragenumberofcarsinline?
a)
It
would
decrease.
b)Itwouldnotchange.
c)Itwouldincrease.
Mr.Ks
Mr.Ksisapopularhairsalon,whichoffershighqualityhairstylingandphysicalrelaxationservices
atareasonableprice.Customersarriveonaverageevery25minutes.
Theyareservedbyoneof3
employees,andthetotalservicetakesonaverage60minutes.
Thecoefficientofvariationofthe
timebetweenarrivalsaswellasthatoftheprocessingtimeis1.2.
a)
Howlongdocustomerswaitonaverage(ifnoneofthemleavesbeforebeingserviced),andhow
manycustomerswillonaveragebewaitingtobeserviced?
b)
Howmanyadditionalserverswouldyouneedtohiresothatcustomerswaitonaverageno
longer
than
10
minutes?
Localbranchofabank
Alocalbranchofabankclaimsthatitscustomerswaitlessthan6minutes(onaverage)inthe
queueduringlunchtime(actually,thisisatwohourperiodbetween11:30and1:30).
Theirrecord
showsthatonaverage60customersarriveduringthetwohourlunchtime.
If7customers(on
average)arewaitinginthequeueduringthisperiod,istheestimateofaveragetimespentinthe
queuerealistic?Justifyyouranswer.
Inventoryturns
Supposeacompanyproduces100,000unitsayearandthattheinventoryturnoverforthiscompany
is40.
Inventory
Turnover
is
defined
as
the
number
of
times
that
acompanys
inventory
cycles
or
turnsperyear.
Whatistheannualinventoryholdingcostofthiscompany,iftheannualholdingcost
perunitis$15?
Maketoorderenvironment
Is the following statement true or false? Why?
In a maketo-order environment, the only viable strategy to
reduce lead-time is to
increase capacity by adding more machines to each station.
7/25/2019 Review Questions Session 3
2/2
NewStationonJubileeLine
ThecityofLondonhasjustdecidedtobuildanewundergroundstationontheJubileeLine,between
BakerStreetandStJohnsWood.ThenewstationlocatedinStJohnsWoodRoad,justopposite
theLordsCricketGround,willonlyservetheJubileeline.
MattRichardsonisinchargeofdesigningthelayoutforthisnewstationandheiscurrentlydealing
withtheplacementofescalators.Duetospaceconstraintsthestationcanaccommodateonlythree
escalators.Hence,
two
configurations
are
possible,
as
indicated
in
the
figure
below.
Whichconfiguration
should
Matt
prefer?
Why?
(Assumethatateverypointintimetheaveragenumberofincomingcustomersisequaltothe
averagenumberofoutgoingcustomers.Assumealsothatallescalatorsmoveatthesamespeedand
thattheplatformandthehallhaveapproximatelythesamesurface).
platform
street
hall
platform
street
hall
CONFIGURATION A:
- 1 UPWARD EXCALATOR
- 2 DOWNWARD EXCALATORS
CONFIGURATION B:
- 2 UPWARD EXCALATORS
- 1 DOWNWARD EXCALATOR
railway railway
