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TT GWD 4-15

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发表于 2006-9-4 18:35:00 | 显示全部楼层

TT GWD 4-15

If n is a positive integer and r is the remainder when (n – 1)(n + 1) is divided by 24, what is the value of r?

(1)     2 is not a factor of n.

(2)     3 is not a factor of n.

                                                                                                                              

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

Answer: C

不懂......

牛牛们教教

发表于 2006-9-4 22:23:00 | 显示全部楼层

我也不是很肯定啊

我觉得2和3都不是N的因数,那么N只能是一个质数且>3,那么(n+1)(n-1)>=24,且每个质数的前后两个数字均含有2和3这两个因数,所以可以被24整除
 楼主| 发表于 2006-9-4 23:09:00 | 显示全部楼层

有人看看么。。。。给个详细的解释

拜托了额

发表于 2006-9-4 23:36:00 | 显示全部楼层

n 不是2和3的倍数,所以只能是6n+1或者6n-1的形式,那么带入(n-1)(n+1),得

(1)6n*(6n+2)=12n(3n+1),其中n(3n+1)必为偶数,所以为24得倍数

(2)类似一的情况可以分析出

所以选C

rr的问:哪里可以找到所有的GWD啊?新手好多都不懂却要9.14上战场了,谢谢~

 楼主| 发表于 2006-9-5 00:36:00 | 显示全部楼层

谢谢了


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