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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.
设拿到白球的可能性是a,拿到双数求的可能性是b 根据条件一,能得出a*b=0,说明a=0,or b=o, or both = 0 然后根据条件二,能得出a-b=0.2 所以根据一跟二我能得出a=0.2 b=0然后a+b就是0.2
可是答案是E,我知道GMAC是不会出错题的,希望有同学能指出我的推理错在什么地方 |
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