求NN继续解释一道PREP数学题

ゞ綵婲尐ㄝ且 · 发表于 2010-8-31 21:01:02

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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

答案选A哈

DennisLeBel · 发表于 2010-8-31 21:21:20

举个极端例子吧,8个homes都是130000，这样满足中位数的要求,然后另外7个homes为了尽可能少,设它们都卖相同价钱X,则X=(150000乘以15-130000乘以8)除以7=17有余...只有A符合了

DennisLeBel · 发表于 2010-8-31 21:22:21

是170000还有余...

ゞ綵婲尐ㄝ且 · 发表于 2010-8-31 21:39:25

o .懂了
谢谢NN

求NN继续解释一道PREP数学题

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