2020－2022新目标英语周报第八期答案

20.【解析】(1)若一次性购买5个甲系列言盒后集齐A1,A2,A3玩偶,则有两种情况①其中一个玩偶3个,其他两个玩偶各1个,则有C0A种结果;………………………(1分)②若其中两个玩偶各2个,另外一个玩偶1个,则共有CC(种结果,……………(2分)故P(E1)=当GN+CCC=90+90=150=59:……11111111(3分)3若一次性购买4个乙系列育盒,全部为B1与全部为B2的概奉相等为,………………(4分)故P(F4)=1………………………………………(5分)(2)①由题可知:-3,………………………(6分)当》≥2时=1-+(1-Q-)=-5=-4(a-1-2(7分)即{Q是以,为首项,以为公比的等比数列(8分)所以Q-3=×(-)=3+请×(-)…(9分)②因为每天购买盲盒的100人都已购买过很多次,所以,对于每一个人来说,某一天来购买盲盒时,可看作n十∞,所以,其购买甲系列的概率近似于÷,…(10分)假设用表示一天中购买甲系列盲盒的人数,则B(10.3),所以E=10×3=40.…(1)分)即购买甲系列的人数的期望为40,所以礼品店应准备甲系列言盒40个,乙系列言盒60个……………(12分)

參考范文about a week later, Pomilla and Andrew got to meet her son'sSavion comilla and Andrew arrived at the metro station at theappointed time, anxiously waiting for Case to come. When Casearrived with a big smile, they felt very happy and excited. Casehugged Andrew warm-heartedly and reached out his right hand, sayingto him. Would you like to take it again?"without hesitation theboy took it and held it firmly. After talking for some time, Pomillatook out the badge and gave it back to Case. Many passengers tookictures of the sceneTaylor Pomilla was moved and expressed her thanks to Caseagain She asked Case how he could calm andrew down at that timeCase told her that he had a daughter with autism and that he hadreceived special training on how to deal with autistic children. Hepromised to visit them often to help Andrew grow up happily. As hewas talking, he took out a police badge that he made by hiimself andgave it to Andrew, who was more than happy to accept it. Ever sincethen they have been friends

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