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[原始] OG16 03和06

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楼主
发表于 2015-11-18 11:23:17 | 只看该作者 回帖奖励 |倒序浏览 |阅读模式
刚开始看OG16的新手,怎么刚开始看就觉得头几道题答案很奇怪,求各位大神指点解惑!谢谢!
OG16 Quantative 03
The sequence A1, A2, A3, . . . ,An, . . . is such that An= (An-1+An-2) /2, n>=3, for all . If A1=4 and A2=20, what is the value of A6?

A. 12 B.16 C. 20 D.24 E.28

答案:E
答案为什么是28?后者为前两数的均值,那么怎么看A6一定是在4和20之前的数字。推算一下,A6应该是15阿。。都不在选项中。。是我哪里审题错了么。。


OG16 Quantative 06
A marketing firm determined that, of 200 households surveyed, 80 used neither
Brand A nor Brand B soap, 60 used only Brand A soap, and for every household
that used both brands of soap, 3 used only Brand B soap. How many of the 200
households surveyed used both brands of soap?

(A) 15
(B) 20
(C) 30
(D) 40
(E) 45

答案:A
题干有句话看不明白,for every household that used both brands of soap, 3 used only Brand B soap 对于每个使用两种soap的household, 有3个只用了brand B?那这句话不是自相矛盾了么。。。晕了。。。


谢谢!
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沙发
发表于 2015-11-18 11:50:43 | 只看该作者
1. 你的題目有錯, 正確: http://gmatclub.com/forum/the-sequence-a1-a2-a3-an-is-such-that-an-an-134498.html
2. for every household that used both brands of soap, 3 used only Brand B soap= 對每一個都用的household, 有3個只用B. (數量上的比較, 前者x, 後者3x)
板凳
 楼主| 发表于 2015-11-18 15:32:01 | 只看该作者
toughbank 发表于 2015-11-18 11:50
1. 你的題目有錯, 正確: http://gmatclub.com/forum/the-sequence-a1-a2-a3-an-is-such-that-an-an-134498. ...

原来如此
谢谢!
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