请教PS

joywzy

13. A company that ships boxes to a total of (12) distribution centers uses color coding to identify  each center. If either a single color or a pair of two different colors is chosen to represent each center  and if each center is uniquely represented by that choice of one or two colors, what is the minimum number of colors needed for the coding ? (Assume that the order of the colors in a pair does not matter.)
   (A) 4  (B) 5  (C) 6  (D) 12  (E) 24
答案:B

16. On a certain road, 10 percent of the motorists exceed the posted speed limit and receive speeding tickets, but 20 percent of the motorists who exceed the posted speed limit do not receive speeding tickets. What percent of the motorists on that road exceed the posted speed limit ?
   (A)          (B)  
   (C) 15%                (D) 22%
   (E) 30%
答案:B

14,14. If the two-digit integers M and N are positive and have the same digits, but in reverse order, which of the following CANNOT be the sum of M and N ?
   (A) 181
(B) 163
   (C) 121
   (D) 99
   (E) 44
答案:A
请问the two-digit integers M and N are positive and have the same digits, but in reverse order有什么特性/

谢谢!

henry_shao

1、我认为答案是C。C2 6=15，可以满足12个组合；C2 5=10，不能满足12 个组合。
2、简单。10%/80%=12.5%
3、本题我以前见过，但现在忘了，好象是选项中不能含有11的因子。请后来者补充。

漫步雨中

13题答案：题的大意是：12个中心，要么用一种颜色，要么用两种颜色的混合辨别它们，求至少需要几种颜色？
设所求为m,则有Cm,2+m>=12,m=5

漫步雨中

14题的答案是不是有问题，我认为A、B都是答案。
因为如果没有进位产生时，个位和十位的数肯定是相等的。
如果有进位产生，那么十位比个位肯定多1,
所以，正如henry所述，选项应该是11的倍数，大家同意吗？是不是B选项是165?

joywzy

能否详细地讲一讲13题？还是不明白。

14，题目就是这样，可能题目错了。

谢谢！