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标题: 这道题答案是不是错了？（已解答） [打印本页]

作者: 灵狩Icy 时间: 2015-5-13 19:27
标题: 这道题答案是不是错了？（已解答）
187. If 0 < r < 1 < s < 2, which of the following must be less than 1 ?
I. r/s
II. rs
III. s-r
                                    (A) I only(B) II only(C) III only(D) I and II(E) I and II

我选的是D，为什么答案是A？？

作者: iriswine 时间: 2015-5-13 19:35
r=0.99, s=1.99 =>rs >1

作者: 灵狩Icy 时间: 2015-5-13 19:46

iriswine 发表于 2015-5-13 19:35
r=0.99, s=1.99 =>rs >1

啊原来可以这么举例。。谢谢！
还有一道题！
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?I.At least one of the homes was sold for more than $165,000.II.At least o
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?
I.At least one of the homes was sold for more than $165,000.
II.At least one of the homes was sold for more than $130,000 and less than $150,000.
III.At least one of the homes was sold for less than $130,000.
A.I only
B.II only
C.III only
D.I and II
E.I and III
这个说答案是A，怎么算的？

作者: iriswine 时间: 2015-5-13 21:14
15个homes，总价格=150,000*15=2250,000
I.
试图满足：1）让总价最大化；2）none of the homes was sold for more than 165,000；3）median是130,000
按从小到大排列，
前7个都取130,000，(为满足条件1)
第八个是130,000 (条件3)
后7个都是165,000 （为满足条件2及条件1）
130*8+165*7=2195 < 2250
所以如果最大值为165,000的话，Max总房价会小于2250,000 与条件矛盾

II. 及III. 举反例即可
反例：前8个 130,000 第9-14个 165,000 第15个：220,000

作者: 灵狩Icy 时间: 2015-5-13 21:39

iriswine 发表于 2015-5-13 21:14
15个homes，总价格=150,000*15=2250,000
I.
试图满足：1）让总价最大化；2）none of the homes was sold f ...

谢谢大神！！好详细！！我更新到我的主题帖啦，谢谢！！
http://forum.chasedream.com/foru ... id=991168&page=

作者: iriswine 时间: 2015-5-13 22:26
Glad it helped.

作者: 灵狩Icy 时间: 2015-5-14 07:11

iriswine 发表于 2015-5-13 22:26
Glad it helped.

大神！！！这里还有两道题。。。。麻烦你啦！！
http://forum.chasedream.com/thread-1002744-1-1.html

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