在线等~~~求大神指点 1+2应该是能推出either white or even的概率吧

lamolee

Each ofthe 25 balls in a certain box is either red, blue, or white and has a numberfrom 1 to 10 painted on it.  If one ballis to be selected at random from the box, what is the probability that the ballselected will either be white or have an even number painted on it?

(1)  The probability that the ball will both bewhite and have an even number painted on it is 0.

(2)    The probability that the ballwill be white minus the probability that the ball will have an even numberpainted on it is 0.2.

lamolee

影子喵 发表于 2017-1-6 16:37
不能得出答案，选E

你可以画个韦恩图，总数是25，一个圆代表white，一个圆代表even，两圆没有交集。你只能 ...

好人一生平安~~~感谢~~

影子喵

不能得出答案，选E

你可以画个韦恩图，总数是25，一个圆代表white，一个圆代表even，两圆没有交集。你只能得出white比even多5个(25*0.2)，那可能性太多了: white 6 & even 1 OR white 7 & even 2 ...