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题库 / Prep2007E1-DS-158
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.
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
题目是问你P(A+B) = P(A) + P(B) - P(AB)
1. P(AB)=0是不充分的.因为如果同时发生的概率为0那么说明白球上都不是偶数,但是不代表不是偶数的都是白球.所以不充分
所以锁定选项B/C/E
2. 白球的概率-偶数概率为0.2,P(A) - P(B) = 0.2 .无法解出 P(A) + P(B)
所以两个加起来也不充分
谢谢！
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