1、GRE数学难题解析,李鼎 南京新东方学校,1. On a certain number line, if -7 is a distance of 4 from n and 7 is a distance of 18 from n then n= (A) 25 (B) 11 (C)- 3 (D) 11 (E)-11,7 is a distance of 18 from n：7到n的距离是187是18到n的距离：7 is the distance of 18 from n,2. How many positive integers less than 20 are equal to the sum
2、 of a positive multiple of 3 and a positive multiple of 4? (A) Two (B) Five (C) Seven (D) Ten (E) Nineteen,3X+4Y20，穷举法（3，6，9，12，15）+（4，8，12，16）20，注意19,d=7.56872 and d1 is the decimal expression for d rounded to the nearest thousandth. 3. The number of decimal places where d and d1 differ 4,B（小于）roun
3、d：四舍五入，d1=7.569,x y and xy0 4. (x+y)/x (x+y)/y,D简化成为y/x和x/y相比，xy0，0xy，x0y（x+y0，x+y0）,5. A positive integer with exactly two different divisors greater than 1 must be (A) a prime (B) an even integer (C) a multiple of 3 (D) the square of a prime (E) the square of an odd integer,不要找反例，而是找选项是否包含所有具有这个性质
4、的数,6. Each of the following numbers has two digits blotted out. Which of the numbers could be the number of hours in x days, where x is an integer? (A)25,06 (B)50,26 (C)56,02 (D)62,50 (E)65,20,能被4整除的数，后两位一定能被4整除24*X然后再看后结果两位数，太麻烦,D，一定不能根据图的表象来判断除非有drawn to scale,8. 4对男女，每对中有1男1女，从每对中选出1人，选出2男2女的概率是多少？,4个男的概率=1/16，4个女的也是3男1女的概率=1/16*4=1/4，3女1男也是2男2女的概率是1-1/16*2-1/4*2=3/82男2女的组合是：C42=6,9.有3个打字员为4家公司服务，如果4家公司各有1份文件要录入，他们只能找到这3个打字员录入，且各公司对打字员的要求是随机的。问每个打字员都收到文件的概率是多少？,4份文件给3个人打，总可能为34=81有两份文件打的人：C31，这两份文件的组合为C42，剩下两人的文件P22概率为C31*C42*P22/81=36/81=4/9,
