2022英语周报答案外研

20.【解析】(1)根据所给数据可得2×2列联表如下潜伏期不低于一周潜伏期低于一周合计男惠者人数(单位:人)402060女患者人数(单位:人)10计100合则x2=10040×30-10×20250=16.67>6635,(3分)60×40×50×503有9%以上的把握认为潜伏期不低于一周(7天)与性别有关:(5分)(2)根据所给数据可知从这100多患者中随机抽取1人其病毒不低于一周(天)的概率为P=501(7分1002随机变量X的可能取值为0,1,2,3,4,∴P(X=0)=(1216,Px=)=C,(-42-2)-3,P(X=3)=C(2)(-=2=,P(x=4)=P(x=2)=C4()216(9分)∴X的分布列如下X041P4由x~B(4.)可得x的数学期望为ECO)、计方差为DO)=4x×(-)=1.(12分)

第三节书面表达wersionDear Sir or MadamMy name is Li Hua. As an exchange student fromChina, I am studying in a local school. I am reallydelighted to learn that a volunteer for your Chinese culturallic exhibition is required and I'm confident that I amtruly fit for thestart with, my advantage first lies in the fact that IChina and used to beand quite familiar with Chinese relics. Further-more, being an outgoing and optimistic boy, I am good atcommunicating with others and introducing Chinese cultureto the world is always my honor and my pleasure. Finallythere is no problem with my spoken English, as I havelived here for almost a year and I have no difficulty commu-dicating with others in EnglishI would really appreciate it if you can offer me thechance to be a volunteer in your museum. I am looking forward to your early reply.Li Hua

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