求Prep题一道

narcissist · 发表于 2008-8-11 15:56:00

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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.

answer is E

Why not B?.....

cambycc · 发表于 2008-8-11 16:07:00

只说明了两者的差，你怎么求出来be white or have an even number painted on it的可能性呢？

所以选择E啊，而且题目太多没有确定的东西。

laipe0704 · 发表于 2008-8-11 16:09:00

題目問說 what is the probability that the ball selected will either be white or have an even number painted on it?
求 p(either white or even)=p(white)+p(even)-p(both)
(1)只得p(both)，不充份
(2)只得p(white)-p(even)，不充份
(1)+(2)也不充份

narcissist · 发表于 2008-8-11 16:30:00

懂了

谢谢大家。。。

求Prep题一道

求Prep题一道

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