这个题是怎么算出来的。。。。

Mia大猫

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.
答案是I,后两个为什么不对？？？

melody56

以前的帖子

median 130位于第八套房，前七套小于或等于130，后七套大于或等于130，平均150。即使前八套房都取130，后七套房也可把前边每套和平均值差值20补回来，故（3）错；同理也可没有房大于130小于150，故（2）错；
关键是（3）考虑到前八套房最多每套售都130，故8*（150-130）=160，假设取最大值，后7套房都为165，7*（165-150）=105，不足以弥补前8套160的差值，故肯定有房大于165
-- by 会员 oceanliuhome (2012/1/16 5:05:44)

thirdwheel

取极端值比如把比中数小的都算成130000 剩下的都是最大的一个值