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.
如题，请教怎么做啊？作者: Vickyliu 时间: 2011-7-17 07:21
1) 2 is not a factor of n. So n is odd. n=1, r =0; n=3, r=8. Insufficient
2) 3 is not a factor of n. So either (n-1) or (n+1) has a factor of 3. n=1, r=0; n=4, r= 15. Insufficient.
1) and 2). So n is odd and n is not a factor of 3. If so, 1) both n-1 and n+1 are even; 2) one of them has a factor of 4; 3) one of them has a factor of 3. So n=2*4*3*m = 24*m. r=0. Sufficient.
