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题库 / GMATAdvanced-PS-61
Which of the following describes the set of all possible values of the positive integer k such that, for each positive odd integer n, the value of ~$n \over k$~ is midway between consecutive integers?
All positive integers greater than 2
All prime numbers
All positive even integers
All even prime numbers
All positive even multiples of 5
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All even prime numbers=2，奇数/2=整数 +0.5
连续的整数的中位数要么是整数+0.5，要么是一个整数，所以奇数/2必定是连续的整数的中位数
小小纠正：连续整数的中位数只能是整数+0.5登录 或 注册 后可以参加讨论
n=aK+0.5K
n是整数推出K=2,4,6...K是偶数，所以aK是偶数
n是奇数，aK是偶数，所以0.5K是奇数，推出K=2
n是一个正奇数，k为正整数，n/k要在两个连续整数的正中间，那就是“X.5”的形式，所以k只能为2，“All even prime numbers”→偶质数就只有2一个，所以答案为D
注意表达： the value of n/k is midway between consecutive integers=值为“x.5",则K一定为2