求解近期几个难题

gmat02

15. 假如X、Y均为正整数，且10＜X＜20, 40＜Y＜60, 那么(XY) ^2的千位数最小是： a. 4，b. 5，c. 6，d. 7，e. 8 [确认]A [思路]最笨的办法：举例。(11*51)^2=314721，正好千位数是4。巧合？ [讨论]是否应该有其他的解法？如果题目问X(Y^2)最小的千位数怎么办？ 96. 一球往下落，碰球往两边落的概率各为1/2, 问该球落到BC间的概率。(3/8) O ▼ O O O O O O O O O O O B C D E [讨论] 3/8 怎么算? 107. 60 cars, either full-size or compact or sports. 31 is white, 10 is red, 19 is blue, how many cars are full-size? (1). Not all red and blue cars are full-size. (2). The number of full-size is greater than the sum of compact and sport cars. [确定]Ans.: C 我认为是E 124. 40% of the total students are from the high-school. Also, 25% of high school students have joined the choir. Now, the total number of students is x. How many high school students are in choir in term of x? [确定]Ans.: 1/10 题目看得不清楚, 有列式否? 126. 一些数S1=3,以后的数是S(N+1)=2S(N-1)-1,求S20-S19的值。 A. 2^19，B. 2^20，C. 2^21，D. 2^21-1，E. 2^20-1 [确定]Ans.：(2^19) 有解题过程吗? 我推不出来 139. On XY plane. If a line goes through Point A (A, 5), Is the slope of the line<0? a. Line goes through (0, -2) b. Line goes through (5, A) [讨论]D 是B吧, 因为可得出SLOPE = -1 145. F(x)=kx^2+mx-1, f(-7)=3, ask f(7)=? [确认]My Ans.: -5 该怎么算, 我求不出 154. 我遇到一题, 我认为可能是题目有误, 也可能是我理解有问题, 我已经报告给了管理员, 大家帮着看一看：题目是: 1994年, 一个公司总共往外发传真80 BILLION, 已知其从1987年开始, 每年发的传真数比上年增长(INCREASED BY )700%, 求其1987年发了多少BILLION传真? 答案最小的是10. 还有11.5等等, 有几十的, 最大的有几百的. 我认为可能是他们把年代搞错了, 这题花了我近10分钟的时间, 以至最后几道题完全没有时间做, 有三道题都是瞎点的. 我数学总共错了四题. [讨论]请大家斟酌。 本题谁有解, 还是题目有错? 碰上了该咋办?