[求助]GMATprep 的题?

GMAT阿驴

IS X-Y>0?

(1)X-Y>2

(2)X-2Y<-6

ANSWER IS C  WHY?

For any positive integer n, the length of n is defined as number of prime factors whose product is n, For example, the length of 75 is 3. Since 75=3*5*5. How many two-digit positive integer have length 6

a.one b, one, c,two ,d.three d. four

answer is C WHY?思路是什么?

谢谢你拉

这套模拟的数学是不是很难的? 我错很多啊  悲

hitlzc

IS X-Y>0?
(1)X-Y>2
(2)X-2Y<-6
ANSWER IS C  WHY?

这个我认为选A啊

For any positive integer n, the length of n is defined as number of prime factors whose product is n, For example, the length of 75 is 3. Since 75=3*5*5. How many two-digit positive integer have length 6
a.one b, one, c,two ,d.three d. four
answer is C WHY?思路是什么?

我是这样考虑的，最小的质数是2，而题目问的length6的，如果都是2的话，那就是2^6=64

再大一点的话，就是2^5*3=96,很明显，再大下去，就大于100了。所以选C

GMAT阿驴

不好意思啊前面抄错拉  应该是X-Y>-2的

IS X-Y>0?

(1)X-Y>-2

(2)X-2Y<-6

ANSWER IS C  WHY?

bewithjessie

假设x=y=10，则两条件均可满足，题干确定不满足。

假设x=11，y=10，则两条件也可满足，题干确定满足。

所以这道题应该是E吧？

期待蔚蓝

同问第一题！

wsdoll

查了破解版，是求 is xy>0.

所以选C.

[此贴子已经被作者于2007-9-10 3:28:15编辑过]

jydemail

wsdoll, 为何是c?

yuanyongchun

x-2y<-6, x-y-y<-6, 设x-y为a， 则a-y<-6, y>6+a

因为a为 x-y>-2, 故 a>-2 ,则 y>4

结合条件1，X-Y>-2, X>Y-2

得出X>2

因为X, Y都大于0

所以XY>0

选C

jydemail

yuanyongchun , top thanks.

tanaka_he

Prep原题应该是这样的

IS XY>0?

(1)X-Y>-2

(2)X-2Y<-6

Answer IS C  

由条件（2）推出：X-Y<Y-6  

联合条件（1）推出：Y-6>X-Y>-2 所以Y>4

同理，由条件（1）推出：X+2>Y>4 所以X>2

Clearly, XY>0

仅供参考～