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/
