求解：GWD数学3

ursula1102

Q14:

How many seconds will it take for a car that is traveling at a constant rate of 45 miles per hour to travel a distance of 22 yards?(1 mile = 1,160 yards)



A.8

B.9

C.10

D.11

E.12

答案：C,     我觉得这道题很奇怪啊，感觉没有答案，我换算得出一点多~~

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：C，我是用举例带数字选出C，怎么算的呢~

doreendu0809

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.


由1得出r为2k+1（k为整），由2得出r为3L+1或者3L-1（L为整）
综合得r为6m+1或者6m-1（m为整）
则（n+1）(n-1)也就是6m(6m+2)或者6m(6m-2)
也就是12m（3m+1）或者12m(3m-1)
如果m是偶数那么m可以被2整除，整个式子也就可以被24整除
如果m是奇数那么3m+1或者3m-1可以被2整除，整个式子也就可以被24整除

ursula1102

哇，懂了懂了~~谢谢~~

yangbaozi

是的，14题我也觉得有问题，算不出选项中的答案，是哪里看错了呢？请高人指点

Rainbeauty

another question（可能有点幼稚）：怎么推出r=2k+1 or 3L-1/3L+1的？