2021-2022英语周报高一课标58期答案

书面表达One possible version:NOTICEA sports meeting will be held in the playground of our school from next Thursday to FridayAs you know, the pressure of study is very heavy now, especially for those senior 3. So the purpose of the sports meeting is to letevery student get relaxed, as a result of which we students can live happily and heal thilyEveryone is welcome to take part in it. Those who perform excellently at the sports meeting will get prizes. But don' t take theresults so serously because taking part is more important than the result. Good luck to everyone!

9.【命题意图】本题考查二项分布以及离散型随机变量的分布列与数学期望解析】(1)由题意可知,随机变量k服从二项分布叫(3),故P()=c(21)()k=0123)则k的分布列为(Ⅱ)①设一个接种周期的接种费用为元则可能的取值为200,300(4分)因为P(E=200)=,P(E=300)=所以E()=200×+300×=275(5分)所以三个接种周期的平均花费为E(X)=3E(E)=3×275=825(6分)②随机变量Y可能的取值为300,600,900设事件A为“在一个接种周期内出现2次或3次抗体,由(1)知,A)=3+=所以P(Y=300)=P(A)(8分)P(Y=600=[1-P(A)]xP(A)=P(y=90(1-P()x(1-(4)1×1=(10分)所以E(Y)=300×-+600×+900×-=525所以E(X)>E(Y)(12分)

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