下列对古典概型说法正确的个数是:①试验中可能出现的基本事件只有有限个;②每个事件出现的可能性相等;③若基本事件总数为n,事件A包括k个基本事件,则P(A)=k/n;;④每个基本时间出现的可能性相等.
C、只有②不正确,注意到古典概型中每个基本事件发生的可能性相等,而不是事件发生的可能性相等。例如抛1颗骰子观察出现的点数,设Ai={出现的点数为i}(i=1,2,3,4,5,6),则Ai为基本事件,每一个基本事件发生的可能性都为1/6;但事...
III.Reading.(2x3=6)GileadSciencesisreportingsomepreliminaryresultsfromtheuseofitsantiviraldrugremdesivirintreatingpatientswithCOVID-19.Thestudy,publishedFridaybytheNewEnglandJournalofMedicine,evaluatedtheresponseof53patientsgivenremdesivironacompassionateusebasis.Thirty-sixshowedclinicalimprovement,whileeightgotworse.Patientswhowerenotonaventilatortendedtodobetterthanthosewhowere.Sevenofthe53died.Allwereinseriousconditionandneededsomekindofoxygensupport,includingmechanicalventilation.ThepatientsreceivedthedrugbetweenJan.25andMarch7ofthisyear.Halfthepatientswerefollowedfor18daysorless.Thepatientswerestudiedinhospitalsaroundtheworld:22intheUnitedStates,22inEuropeorCanadaand9inJapan.Morethanhalfthepatientsinthestudyexperiencedsideeffectfromthedrug,rangingfromarashanddiarrheatoacutekidneyinjury.Astheauthorsnote,severalfactorsmakeithardtointerprettheresultsonthestudy.Thesmallnumberofpatients,therelativelyshortdurationofthefollow-upandthelackofacontrolgroup—peoplewhoreceivedaplaceboinsteadoftheactivedrug.Severallargecontrolledstudiesareunderwaythatcouldprovidemoredefinitiveevidenceofwhetherthedrugisusefulornot,andunderwhatcircumstances.11.Whatisremdesivir?