扫描二维码，直接登录
题库 / Prep2007E2-DS-21
Is the integer n odd?
(1) n is divisible by 3.
(2) 2n is divisible by twice as many positive integers as n.
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.
还没有题目讲解（毕出老师会陆续发布对官方考题的解读，请保持关注）。
有一个思路： 不知道n为奇还是偶，假定n有因子：a1，a2，a3 。。。an
那么2n的因子就为：a1，a2, a3... an, 2a1, 2a2, 2a3...2an
新增加的因子有2a1, 2a2, 2a3... 2an，因为条件为刚好2倍。说明新增加的因子中无重复，那么原先的因子中就必然不能有2。
因为一旦有2，就至少有1x2=2，和之前的2重复了，因子数就会小于2倍。既然不能有2 ，那就必然为奇数
登录 或 注册 后可以参加讨论