逻辑答案部分 Wiley.The.Official.Guide.For.GMAT.Review.12th.Edition.pdf

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1、TheOfficialGuideforGMAT®Review12thEdition8.6AnswerExplanationsThefollowingdiscussionisintendedtofamiliarizeyouwiththemostefficientandeffectiveapproachestocriticalreasoningquestions.Theparticularquestionsinthischapteraregenerallyrepresentativeofthekindsofcriticalreasoningquestionsyouwille

2、ncounterontheGMAT.Rememberthatitistheproblemsolvingstrategythatisimportant,notthespecificdetailsofaparticularquestion.1.“Lifeexpectancy”istheaverageageatdeathoftheentirelive-bornpopulation.Inthemiddleofthenineteenthcentury,lifeexpectancyinNorthAmericawas40years,whereasnowitisnearly80yea

3、rs.Thus,inthosedays,peoplemusthavebeenconsideredoldatanagethatwenowconsidertheprimeoflife.Whichofthefollowing,iftrue,underminestheargumentabove?(A)Inthemiddleofthenineteenthcentury,thepopulationofNorthAmericawassignificantlysmallerthanitistoday.(B)Mostofthegainsinlifeexpectancyinthelast

4、150yearshavecomefromreductionsinthenumberofinfantswhodieintheirfirstyearoflife.(C)Manyofthepeoplewholivetoanadvancedagetodaydosoonlybecauseofmedicaltechnologythatwasunknowninthenineteenthcentury.(D)Theproportionofpeoplewhodieintheirseventiesissignificantlysmallertodaythanistheproportiono

5、fpeoplewhodieintheireighties.(E)Morepeopleinthemiddleofthenineteenthcenturyengagedregularlyinvigorousphysicalactivitythandosotoday.ArgumentEvaluationSituationLifeexpectancyinmid-nineteenthcenturyNorthAmericawas40years;nowitisalmost80.Whatwethinkofastheprimeoflifemusthavebeenconsideredo

6、ldinthatearlierera.ReasoningWhatpointweakensthisargument?Theargumentisdiscussinglifeexpectancyovertheentirepopulationofthosebornalive.Theargumentreliesontheideathatif40yearswastheaveragelifeexpectancy,thentheusuallengthoflifemusthavebeenaround40.Butaveragescanbemisleading.Whatif,inthen

7、ineteenthcentury,thenumberofinfantsbornalivebutnotsurvivingtheirfirstyearwasfarhigherthanitistoday?Ifthiswereso,itwouldsignificantlyreducetheaverageageattimeofdeathofthepopulationasawhole—butofcoursethatpopulationcouldhavecontainedmanywholivedwellintotheirseventiesoreighties.Thus,ifwea