GMATPrep Practice 1 数学 16 请教

if xy=1, what is the value of 2(x+y)²/2(x-y)²?

answer: 16

怎么算不出来啊,请指教!

另外数学26:

At least 100 students at a certain high school study Japanese. If 4 percent of the students who study French also study Japanese, do more students at the school study French than Japanese?

1)16 students at the school study both French and Japanese.

2)10 percent of the students at the school who study Japanese also study French.

answer: 2) is sufficient, but 1) is not.

问题:怎么觉得1)也可以呀?1)不是能算出学法语的是64人吗?

请指点!

第一题要么有误，要么条件不足吧。

第二题第一个条件算出的学法语学生是400个，而学日语学生至少100个，无法判断哪个更多，此条件不足。

请问题目2中为何条件2是充分的？不知道学生总数，也不知道多少人2门语言都没学，如何比较呢？

假设同样一个数量的东西

在a里能占到10％

在b里才能占到4％

两个集合谁大？

关于第一题...虽然这题错了..但是我们以后碰到这种情况即:给出几个未知数的关系,然后求一个代数值..可以取特殊值.使得前面的关系满足..然后代到后面的代数值中取运算..

例如这题取X=2   Y=1(注意这题是错的哦)

谢谢大家的回复.

第2题是我太粗心了,把4%看成1/4了.恨..ing

第1题我也觉得题目错了,但作时看了几遍,题目就是这样的.这个GMATPrep是新东家的题,可能他们还在摸索着.

At least 100 students at a certain high school study Japanese. If 4 percent of the students who study French also study Japanese, do more students at the school study French than Japanese?

1)16 students at the school study both French and Japanese.

2)10 percent of the students at the school who study Japanese also study French.

answer: 2) is sufficient, but 1) is not.

能否再解释一下,我怎么还是不懂.感觉这条件都给的重复了.谢谢了

以下是引用shamoguzhou在2006-3-9 23:43:00的发言：

At least 100 students at a certain high school study Japanese. If 4 percent of the students who study French also study Japanese, do more students at the school study French than Japanese?

1)16 students at the school study both French and Japanese.

2)10 percent of the students at the school who study Japanese also study French.

answer: 2) is sufficient, but 1) is not.

能否再解释一下,我怎么还是不懂.感觉这条件都给的重复了.谢谢了

不一样的，题干是说学法语中有4％的人学日语，学日语的人中有10％学法语

who study xxx是定语从句，also study xxx是谓语，不是并列关系。