题目
题型:不详难度:来源:
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(I)求这三个电话是打给同一人的概率;
(II)求这三个电话中恰有两上是打给乙的概率;
(III)设三个电话中打给乙与丙的个数差的绝对值为X,求X的分布列和E(X).
答案
所求概率为:p=(
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(Ⅱ)这是n=3,p=
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故所求概率为:P3(2)=
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(III)X的取值分别为0,1,2,3
P(X=0)=(
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P(X=2)=3(
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