[求助]几道PREP数学题。谢谢大家

yifeir

1 、On a certain sight-seeing tour, the ratio of the number of women to the number of children was 5 to 2.  What was the number of men on the sight-seeing tour?

 

(1)  On the sight-seeing tour, the ratio of the number of children to the number of men was 5 to 11.

 

(2)  The number of women on the sight-seeing tour was less than 30

答案选C。为什么啊？我怎么觉得条件不够呢？女人只是比30人少怎么会求出具体人数呢？？

2、

Last month 15 homes were sold in Town X.  The average (arithmetic mean) sale price of the homes was $150,000 and the median sale price was $130,000.  Which of the following statements must be true?

   （1）At least one of houses was sold for more than 165000

     (2)at least one home sold for more than 130000 and less than 150000

     (3)at least one home sold for less than 130000
      

(A) I only

(B) II only

(C) III only

(D) I and II

(E) I and III

答案选A，不明白。

3

165.    16466-!-item-!-187;#058&010795

Of the 1,400 college teachers surveyed, 42 percent said that they considered engaging in research an essential goal.  How many of the college teachers surveyed were women?

 

(1) In the survey, 36 percent of the men and 50 percent of the women said that they considered engaging in research an essential goal.

 

(2) In the survey, 288 men said that they considered engaging in research an essential goal.

答案选A，我选C。如果不知道男的，怎么知道总数？

165.    16466-!-item-!-187;#058&010795

Of the 1,400 college teachers surveyed, 42 percent said that they considered engaging in research an essential goal.  How many of the college teachers surveyed were women?

 

(1) In the survey, 36 percent of the men and 50 percent of the women said that they considered engaging in research an essential goal.

 

(2) In the survey, 288 men said that they considered engaging in research an essential goal.

答案选A，我选C。如果不知道男的，怎么知道总数？

谢谢大家。本人DS比较弱，想不通这几个题，麻烦大家给解释下这几道题目。

yifeir

自己顶起来

quietliu

以下是引用yifeir在2008-8-10 21:44:00的发言：

1 、On a certain sight-seeing tour, the ratio of the number of women to the number of children was 5 to 2.  What was the number of men on the sight-seeing tour?

(1)  On the sight-seeing tour, the ratio of the number of children to the number of men was 5 to 11.

(1)  On the sight-seeing tour, the ratio of the number of children to the number of men was 5 to 11.

(2)  The number of women on the sight-seeing tour was less than 30

答案选C。为什么啊？我怎么觉得条件不够呢？女人只是比30人少怎么会求出具体人数呢？？

那个比例有了，但还要求人都是整数，那么条件二就要求女的是五的倍数，你再想想，所以只能用25。要不算不出男的人数。不取25男人不是整数。我这么想的，不知道有什么解法。

2、Last month 15 homes were sold in Town X.  The average (arithmetic mean) sale price of the homes was $150,000 and the median sale price was $130,000.  Which of the following statements must be true?

   （1）At least one of houses was sold for more than 165000

     (2)at least one home sold for more than 130000 and less than 150000

     (3)at least one home sold for less than 130000
      

(A) I only（中值前面取与中值相同，那么后面的数都取相同，后面的数就是要求的最小值，必须有一个数要大于这个数，即8*130+7*X=15*150，X=164.444多少，所以A对）其它两个没有一定的要求的，不要求在中值的平均值中间有数，也不要求有比中值小的，你想想，1中就没有2和3两种情况，所以2、3不一定要。

3

165.    16466-!-item-!-187;#058&010795

Of the 1,400 college teachers surveyed, 42 percent said that they considered engaging in research an essential goal.  How many of the college teachers surveyed were women?

(1) In the survey, 36 percent of the men and 50 percent of the women said that they considered engaging in research an essential goal.

（利用1400，就可以列出方程求了（1400-X）36%+X*50%=1400*42%）

（利用1400，就可以列出方程求了（1400-X）36%+X*50%=1400*42%）

（利用1400，就可以列出方程求了（1400-X）36%+X*50%=1400*42%）

(2) In the survey, 288 men said that they considered engaging in research an essential goal.（288，相当于只给了男的比例，则条件就不够了）

165.    16466-!-item-!-187;#058&010795

Of the 1,400 college teachers surveyed, 42 percent said that they considered engaging in research an essential goal.  How many of the college teachers surveyed were women?

(1) In the survey, 36 percent of the men and 50 percent of the women said that they considered engaging in research an essential goal.

（利用1400，就可以列出方程求了（1400-X）36%+X*50%=1400*42%）

（利用1400，就可以列出方程求了（1400-X）36%+X*50%=1400*42%）

（利用1400，就可以列出方程求了（1400-X）36%+X*50%=1400*42%）

(2) In the survey, 288 men said that they considered engaging in research an essential goal.（288，相当于只给了男的比例，则条件就不够了）

[此贴子已经被作者于2008-8-10 23:51:52编辑过]

quietliu

好像电脑有点问题，那些重复的也删除不掉，将就看吧。

yifeir

以下是引用quietliu在2008-8-10 23:53:00的发言：
好像电脑有点问题，那些重复的也删除不掉，将就看吧。

不是电脑的问题，是论坛好像设置的问题，我的题目也有重复的，而且编辑不下去。Anyway，多谢多谢。呵呵。祝你申请成功！