prep test1-8我没在讨论贴里找到，所以请大家来解答一下

以下是ＰＲＥＰ　ＴＥＳＴ１　ＮＯ８的ＤＡＴＡ　ＳＵＦＦＩＣＩＥＮＣＹ的题目

Each of the 25 balls in a certain box is either red, blue, or white and has a number form 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

像这类题目有什么技巧吗？

答案是E吧。题目求的是W+E-W∩E （white, even number）

条件1只能确定white 和even number 没有交集。即W∩E等于0.

条件2只能确定两者的差。

两条件同时也不能确定W+E是多少。