金爱妍
幼苗
共回答了14个问题采纳率:92.9% 举报
(1) 0.21 p=0.4
(1)由0.2+0.3+p+0.1=1,得p=0.4.
设甲,乙两人击中的环数分别为X
1 ,X
2 ,则
P(X
1 =8)=
=0.1,
P(X
1 =9)=
=0.2,
P(X
1 =10)=
=0.4;
P(X
2 =8)=0.3,
P(X
2 =9)=0.4,
P(X
2 =10)=0.1,
所以甲,乙各打一枪共击中18环的概率为:
P=0.1×0.1+0.3×0.4+0.2×0.4=0.21.
(2)甲的期望E(X
1 )=5×0.1+6×0.1+7×0.1+8×0.1+9×0.2+10×0.4=8.4.
乙的期望E(X
2 )=7×0.2+8×0.3+9×0.4+10×0.1=8.4.
甲的方差D(X
1 )=(5-8.4)
2 ×0.1+(6-8.4)
2 ×0.1+(7-8.4)
2 ×0.1+(8-8.4)
2 ×0.1+(9-8.4)
2 ×0.2+(10-8.4)
2 ×0.4=3.04.
乙的方差为D(X
2 )=(7-8.4)
2 ×0.2+(8-8.4)
2 ×0.3+(9-8.4)
2 ×0.4+(10-8.4)
2 ×0.1=0.84.
由于D(X
1 )>D(X
2 ),故乙比甲技术稳定.
1年前
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