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下面GMAT思为大家整理了GMAT数学备考资料：练习+讲解（7），供考生们参考，以下是详细内容。 1、In an insurance company, each policy has a paper record or an electric record, or both of them. 60 percent of the policies having incorrect paper record have incorrect electric record and 75 percent of the policies having incorrect electric record have incorrect paper record. 3 percent of all the policies have both incorrect paper and incorrect electric records. If we randomly pick out one policy, what is the probability that it is one having both correct paper and correct electric record? 【答案】94% 【思路】 设总数为X policies，则既有非P又有非E为3%X;60%的非P中为非E，则非P为3%X/60%;75%的非E为非P，则非E为3%/75%，那么非P与非E一共有 ，那么P与E一共有X-，则其概率为/X=94% 2、If for all x, x^2+ax+b = ^2, then a =? b=0; c=-3; 【答案】B 【思路】x^2+ax+b = ^2= x^2+2cx+c^2，则A=2C，只要知道C的值就可以知道A值了 x^2+ax+b = ^2= x^2+2cx+c^2 x^2+ax+b = x^2+2cx+c^2 化简后：x+=0 因为对于所有的x值，上式均成立，则a-2c与b-c^2必须同时为0; a-2c=0 | 
