what is the probability of getting a total of 9 for 6 tosses of a pair of dice A.twice B.at least不是翻译,两个骰子掷6次 情况1:两次为9的概率是多少; 情况2:至少两次为9.,应该是中文意思,求各种方法详解.
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what is the probability of getting a total of 9 for 6 tosses of a pair of dice A.twice B.at least
不是翻译,两个骰子掷6次 情况1:两次为9的概率是多少; 情况2:至少两次为9.,应该是中文意思,求各种方法详解.
用二项式概率做吧.
1) 数出有多少种可以得9的可能,分别为(6,3) (3,6), (5,4), (4,5) 四种,那么掷出9的可能就是9/36, = 1/4, 不掷出9的概率就是3/4. 我们要在6次中成功两次,既然顺序不要紧(在第几次掷出9不要紧),就可以用组合.
C(6,2) x (1/4)^2 x (3/4)^4 = 1215/4096
第一个C(6,2)是从6次投掷中取2次成功,之后成功的两次的概率各是1/4, 其他的概率有4次不成功.
2)总概率是1, 之后减去没有9和只有一个9的概率即可.
1 - (3/4)^6 - [ C(6,1) x (1/4)^1 x (3/4)^5 ] = 1909/4096
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