8. A box contains 100 balls, numbered from 1 to 100. If three balls are selected at random and with replacement from the box,what is the probability that the
sum of the three numbers on the balls selected from the box will be odd?
(A) 1/4
(B) 3/8
(C) 1/2
(D) 5/8
(E) 3/4
9. (0-9) 要组成三位电话号码,第一位不能是0或1,三位数中相邻两位不能为同一数. (e.g. 227 not acceptable,but 272 acceptable),求可以组成多少个这样的电话号
码?
10. 从1,2,3,4,5,6,7,8,9中选出三个数字组成一个三位数,这个三位数的digits中有两个相同,另一个digit与其它两个都不同,问共有多少个这样的三位数?
(A) 72
(B) 144
(C) 180
(D) 216
(E) 54
11. A,B,C,D,E,F排在1,2,3,4,5,6六个位置上,问A不在1, B不在2, C不在3的情况下,共有多少种排法?
(A) 720
(B) 450
(C) 180
(D) 216
(E) 320
12. 一直线L过点A(5,0), B(0,2), 坐标原点为O, 点P(X,Y)为三角形OAB中一点, 问:Y
(A) 1/4
(B) 3/8
(C) 1/2
(D) 5/8
(E) 3/4
13. If Bob can do a job in 20 days and Jane can do the job in 30 days, they work together to do this job and in this period, Bob stop work for 2.5 days and
Jane stop work for x days, and the job be finished for 14 days, what is x?
(A) 1.6
(B) 3.2
(C) 1.5
(D) 1.25
(E) 1.15