[求助]涛涛数学题

luqiao0709

Q16:

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.

答案选C

shiverson

这题以前有讨论过吧我记得...

先算1，因为特殊，余0

然后2不是因子，说明比如n=3、5、7、9等等这些数的时候，余数r分别为8，0，0，0

然后3不是因子，说明比如n=2，4，5，8等等这些数的时候，余数r分别人3，15，0，15

但要是结合起来，既不是2，也不是3为因子的，就只有比如n=5，11，13，17这样的数，但是这样的数就把唯一一个有余数的n=3给排除了(因为n=偶数也都被排除了)所以余数只能为0

luqiao0709

谢谢！！