There are five cards marked 1, 2, 3, 4, 5 in a box. If the sum of two cards which are taken from those cards randomly (no replac

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问题 There are five cards marked 1, 2, 3, 4, 5 in a box. If the sum of two cards which are taken from those cards randomly (no replacement) is even. What is the probability that these two cards are both odd?

选项 A、1/4
B、3/4
C、3/10
D、3/5
E、1/3

答案B

解析 本题求的是取出两数和为偶数的情况下,两数都是奇数的概率。而不是说取出两数,两数都是奇数的概率。注意,由于取出数是no replacement,因此是“无放回的取法”,取出的两个数不相同。在偶数:奇数+奇数的情况中,共有1,3,5三个奇数,取出两个,C32=3种取法。在偶数:偶数+偶数的情况中,共有2,4两个奇数,取出两个,只有1种取法。因此所求概率是3/(3+1)=3/4。
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本试题收录于: GMAT QUANTITATIVE题库GMAT分类
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