求解一道DS题！！谢谢！

Seajinking · 发表于 2015-9-27 15:31:38

Each of the 25 balls in a certain box is either red, blue, or white and has a number from 1 to 10 painted on it. If one ball is
to be selected at random from the box, what is the probability that the ball selected will either be white or have an even
number painted on it?
(1) The probability that the ball will both be white and have an even number painted on it is 0.
(2) The probability that the ball will be white minus the probability that the ball will have an even number painted on it is
0.2.

这种题目怎么很快做出判断？因为选的时候一直在犹豫是自己不会还是算不出。。。

P.S.能推荐一下关于概率比较好的讲解吗？本人一碰上概率就抓瞎

guoyilin2015 · 发表于 2015-9-27 22:46:48

R Red
B Blue
W White
O Odd
E Even

RO+RE+BO+BE+WO+WE=25，求WE+WO+BE+RE
(1) WE=0
(2) WE+WO-RE-BE=5

C
求WO+BE+RE
BE+RE+5=WO

求2WO-5
WO未知
E

这里BE,RE和BO,RO可以视为一体，因为题目并没有对它们作区分

guoyilin2015 · 发表于 2015-9-27 22:47:39

https://www.manhattanprep.com/gmat/forums/each-of-the-25-balls-in-a-certain-box-is-either-red-blue-or-t308.html

这里RON大神用的矩阵法也很不错的

tophoenix · 发表于 2015-9-27 23:45:12

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狗狗AGO · 发表于 2019-11-8 08:55:33

guoyilin2015 发表于 2015-9-27 22:46
R Red
B Blue
W White

Mark一下！

求解一道DS题！！谢谢！

所属分类: GMAT考试

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tophoenix tophoenix 当前离线 UID 400825 在线时间小时注册时间 2008-11-30 最后登录 1970-1-1 主题帖子性别保密	地板发表于 2015-9-27 23:45:12 \| 只看该作者提示: 作者被禁止或删除内容自动屏蔽

	回复同意！看一下！ Mark一下！举报