北美22号2战，数学51。放狗~~（数学部分）

jingqh

lz一战只准备了10来天，640惨败而归；二战准备时间仍只有10天（对自己无语），今早8点就去考了，结果690......
考虑要不要考第三次。因为很想上Vanderbilt的MSF，不上700估计是没戏的。
总之数学不难，好些JJ的题。我整理了一下考场碰见的与JJ有差异或是JJ里不清楚的几道。 （附件里有图）

7. V1   联合两个条件的确可以求出m=n=0，但n不能等于0。
故选E。

42. V2   注意与V1不同的是有一个附加条件：when the tank was pumped to 2000 gallon water, the pumper stopped. 其他数据与机经V2一样。
此题选A。

72. 我遇到的题目如下：
如图（有点丑哈），?Triangle ABC and ?its similar Triangle DEF are isosceles triangles. AB=AC, DE=EF. BR and DS are perpendicular to AC and EF. AC=12, ES=3. What’s the perimeter of Triangle DEF?
(1) BR=8
(2) DS=6
此题选D。

131. S0, S1, S2…Si is a sequence, and S0=0. Can you calculate the value of S10?
(1) For any i≥1, Si is greater than S(i-1) by 4;
(2) For any i≥1, Si + S(i-1) = i2.
这道题选D， 两者皆sufficient。

142 & 336. Both k and n are positive integers. Is k a factor of n?
(1) 根号下(2 – k) = k
(2) (3-n) ^2 = n – 2
此题选C。 注意由条件1可得k = -2 或 k = 1。我差点选了E，但再一想k 是正整数，所以得舍去k = -2。故无论n取何值k = 1必是其因子。

144. 我遇到得问题是问how many people only saw two movies? 其他数据和V3一样。
答案是20。

190. 变体：A list of four positive integers whose median and mean are both 80. What’s the range of this list of numbers?
(1) The least number in the list is 40 (具体数目不太记得了);
(2) The sum of the least and the greatest numbers is 160
此题选A。

254. 变体，题目里没有告诉任何值或比例关系，只是单纯地描述图而已。大概是：Circle O1 has a concentric circle whose center pass through Point C. Circle C circumscribe Circle O1 at Point B. A rectangle ACDE passes through Point C and B, and intersects Circle O1 at Point A. What’s the area of the shaded part?
(1) The area of the rectangle is ** (是个具体的数，不记得了)
(2) The area of Circle C is 9π
此题选A。

260. 补充题目：Two integers x and y. Is xy^2 > 0?
(1) xy < 0
(2) x^2y > 0
此题选C。
?    还有一道是和这题类似，但x、y反过来的。大概是：Tow integers x and y. Is x2y < 0?
(1)    xy > 0
(2)    xy2 < 0
同样选C。

303. V2   并没有说X是integer。

317. The sales from 1994 to 1995 increased by 300%. What is the ratio of sales in 1995 to those of 1994?
答案是4:1。

324. a, b, c, d are integers (或者是real numbers， 不影响). Is a/b + c/d > 2?
(1) a > b
(2) d > c
此题选E。

另外补充一道集合的题。
In a school there are 46 (这个数不太确定，但肯定是四十几) students choosing to learn Statistics and 49 chose Computer Science. 40 students chose both. What’s the number of students who only chose one of them but not both?
答案是15。

wtorchid

谢谢分享！142根据你的分析，不选A吗？

jingqh

谢谢分享！142根据你的分析，不选A吗？

-- by 会员 wtorchid (2012/2/23 6:00:57)

我没想到给...你这么一问，好像也对。现在我觉得应该选A。我只拿到98%，估计这题错了。