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1袋中放有3个红球,2个白球,第一次取出一球,不放回,第二次再取一球,则两次都是红球的概率是( )。
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B.
C.
D.
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2掷两颗均匀的骰子,事件“点数之和为3”的概率是( )。
A.
B.
C.
D.
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3设随机事件
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满足
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,则( )。
A.
互为对立事件
B.
互不相容
C.
一定为不可能事件
D.
不一定为不可能事件
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4在事件A,B,C中,A和B至少有一个发生而C不发生的事件可表示为( )。
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;
B.
;
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;
D.
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.
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5设
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,则
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表示( )。
A.
B.
C.
D.
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6A、B为两事件,若
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,则( )。
A.
B.
C.
D.
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7有6本中文书和4本外文书,任意往书架摆放,则4本外文书放在一起的概率是( )。
A.
B.
C.
D.
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8设A、B为两个事件,
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,且
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,则下列必成立是( )。
A.
B.
C.
D.
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9设盒中有10个木质球,6个玻璃球,木质球有3个红球,7个蓝色;玻璃球有2个红色,4个蓝色。现在从盒中任取一球,用A表示“取到蓝色球”,B表示“取到玻璃球”,则P(B|A)=( )。
A.
B.
C.
D.
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10设A、B为两事件,且
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均大于0,则下列公式错误的是( )。
A.
B.
C.
D.
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