从1,2,3,4,5,6,7,8,9中任意选出三个数,使它们的和为奇数,共有几种不同的选法?
2023-06-11
A. 44
B. 43
C. 42
D. 40
参考答案:D
B. 43
C. 42
D. 40
参考答案:D
解题指导: 三个数的和为奇数,有两种组合法:三个奇数、两个偶数一个奇数;C(3 5)+C(1 5)C(2 4)=5×4×3/2×1+5×4×3/2=40,故答案为D。
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