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标题: GWD3-30 [打印本页]

作者: poorleafs 时间: 2005-10-4 12:20 标题: GWD3-30

Q30:

M = {-6, -5, -4, -3, -2}

T = {-2, -1, 0, 1, 2, 3}

If an integer is to be randomly selected from set M above and an integer is to be randomly selected from set T above, what is the probability that the product of the two integers will be negative?

A. 0

B. 1/3

C. 2/5

D. 1/2

E. 3/5

我只会用穷局法，好累，而且算不出结果，有更好的办法么？我算出来是11/20?

作者: sammen 时间: 2005-10-4 14:02

要求是乘积是负的,那么2个数一正一负.

作者: nbnhjf 时间: 2005-10-5 06:20

从M中任选一个是负数, 而要满足2个数的乘积是正,则只要考虑从T中选出负数的概率. 很容易得出是1/2.

作者: recently 时间: 2005-10-6 06:21

I think that the answar is E.

the total choice= C51*C51=25

and if the product is negative, the choice is C51*C31=15

so the probability is 15/25=3/5

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