prep 中几道搞不清的题目 1

helenlife

Trying to understand why the answer is E.


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.

avalon9527

个人理解：题目是问白球或者双数球的概率。照意思应该是求 白色球/25 + 双数球/25 =？
1)白色球没有双数球
2)白色球的概率减双数球的概率等于0.2
就算联立也不能得出答案。完全可能A.白色球都是单数，且有10个，双数球有5个，但都是红色，10个蓝色球都是单数；或B.白色球有11个，且都为单数，双数球有6个，都是蓝色，8个红色球都是单数。