统计概率A test consists of 20 multiple choice questions.Each que

统计概率
A test consists of 20 multiple choice questions.Each question has 5 possible answers,of which only one is correct.If a student guesses on each question,find the following：
1) estimate the probability of the number of correct answers that will fall within the limits μ±3σ
沙漠之南 1年前 已收到1个回答 举报
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jimhawl 幼苗

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设X为‘the number of correct answers’
X服从n=20,p=1/5的二项分布,即B(20,1/5）,分布律为
P(X=k)=C(20,k)*(1/5)^k*(1-1/5)^(20-k),k=0,1,2,…20
μ=EX=np=4
σ=√DX=√np(1-p)=4√5/5
P(μ-3σ

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