[问答] 求助从GRE部分数学真题里的问题 [复制链接]

sakurajb
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电梯直达

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发表于 2012-3-16 13:49:36 |只看该作者 |倒序浏览

昨天发了个帖子，谢谢耐心给我解答
我在做过去大家讨论过的真题，好多不确定的，麻烦再看一下，非常感谢！
3. A and B are independent events, p(A)=0.6 p(B)=0.8
what is the probability of happening event A or B?
我觉得既然是independent，那p(A and B) = 0
这样就大于1了，不可能的。。

12. In a room there are more than 12 members which are divided into a 5 member group and a 8 member group and a 12 member group.
Find the least possible members in that room such that finally none were left?
guess the members in the room
这个题我读了不懂什么意思

Thursday Nov 22, 2007
8. On a street, there are 4houses which are to be painted. There is a choice of three colors, and one house will be painted with a single color. In how many ways can the houses be painted?

这个题我想先选颜色，3个里面挑1个，完后在4个房子里做排列
（3C1）4*(2C1)*3*2
但是结果不对

谢谢有耐心帮我解答问题

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watertcafe
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沙发

发表于 2012-3-16 13:58:27 |只看该作者

亲……
“我觉得既然是independent，那p(A and B) = 0”
这个错了……
应该是0.6x0.8=0.48，独立事件同时发生的概率就是二者概率相乘
AorB发生概率应该是1-P（A)P(B)-P(A-)P(B-)=1-0.6X0.8-0.4X0.2=0.44

第三题就是3的4次方=27吧
每个房子从三个颜色里挑一个，然后有四个房子