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GRE考试中，虽说考生在GRE数学部分有着很大的优势，但对于复习也不能轻视，要把这个优势发挥最大的作用，提升GRE成绩，下面是GRE数学模拟练习题。 1. 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? 720 450 180 216 320 2. 一直线L过点A, B, 坐标原点为O, 点P为三角形OAB中一点, 问:Y 1/4 3/8 1/2 5/8 3/4 3. In an insurance company, each policy has a paper record and an electric record. For those policies having incorrect paper record, 60% also having incorrect electric record; For policies having incorrect electric record, 75% also having incorrect paper record. 3% of all policies have both incorrect paper and incorrect electric records. If we randomly pick out one policy,whats the probability that the one having both correct paper and correct electric records? 0.80 0.94 0.75 0.88 0.92 4. 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? | 
