试卷总共有5道选择题,其中只有一个答案是正确的.如果每题都是-查字典问答网

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　　试卷总共有5道选择题,其中只有一个答案是正确的.如果每题都是随机选择一个答案,求答对题数X的概率分布及至少答对两题的概率

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2020-04-20 00:37

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陈武凡

　　答对0个是:C50(其中5是下标,1是上标,下同）*(3/4)*(3/4)*(3/4)*(3/4)*(3/4)=243/1024

　　答对1个是:C51*(1/4)*(3/4)*(3/4)*(3/4)*(3/4)=405/1024

　　答对2个是:C52*(1/4)*(1/4)*(3/4)*(3/4)*(3/4)=270/1024

　　答对3个是:C53*(1/4)*(1/4)*(1/4)*(3/4)*(3/4)=90/1024

　　答对4个是:C54*(1/4)*(1/4)*(1/4)*(1/4)*(3/4)=15/1024

　　答对5个是:C55*(1/4)*(1/4)*(1/4)*(1/4)*(1/4)=1/1024

　　至少答对2个题：即为至多答对一个的反面,即1-答对1个的概率-答对0个的概率=1-243/1024-405/1024=376/1024=47/128

2020-04-20 00:42:53