SDCAR2010【逻辑入门】（八）Assumptions

sdcar2010

Necessary.

Sufficient assumption ALWAYS has the word IF in the question stem.

wsyzzydy

thanks. your method really makes the assumption question simple~

泾渭不凡

DING出来明天才能做笔记哇~~~~~~~~~~

泾渭不凡

SDCAR2010【逻辑入门】（八）Assumptions

   假设是木有明确阐明的前提条件，即为作者没有明确说明的但是支持结论的部分条件。

充分VS.必要假设：

     假设你被控诉在GMAT考试过程中涉嫌抄袭。在全体陪审团的听证会上，只有一个证据被提供——你的一句证词：“我没有作弊。”在听讯你的证词之后，陪审团得出结论：你没有作弊。你很高兴。但是从逻辑上来讲，由于他们假设你的话是真的，他们的结论是不牢靠的。事实上陪审团至少有三种假设：
1、你说的是实话。
2、你在听证会上说的是实话。
3、你有可能说的是实话。
     析：第一个是充分假设。但是它不是必要假设或是我们必须得出的假设，因为——————

teddybearj4

在这先谢过sdcar2010大神了，你在很多帖子上很多一针见血的精彩解答都让我受益匪浅。
最近重新看OG上的逻辑，试图在每种分类里面把之前看的包括你还有很多NN的中方法操练变成自己的方法，但是在assumption的中取非得运用中时常有些疑问，取非之后经常脑袋就被几个not绕不清楚到底weaken了没有。首先正确答案取非一定是对conclusion的削弱，然后我自己总结了一下非正确答案取非有几种情况：题目本身范围扩大，取非了之后与conclusion无关，或者是问题事实的重复，或者是无法削弱conclusion。不知道可不可以这样理解，或者是应该怎么想呢？
谢谢sdcar2010！！！

米米时代007

The U.S. census is not perfect: thousands of Americans probably go uncounted. However, the basic statistical portrait of the nation painted by the census is accurate. Certainly some of the poor go uncounted, particularly the homeless; but some of the rich go uncounted as well, because they are often abroad or traveling between one residence and another.

Which of the following is an assumption on which the argument above depends?

(A) Both the rich and the poor have personal and economic reasons to avoid being counted by the census.
(B) All Americans may reasonably be classified as either poor or rich.
(C) The percentage of poor Americans uncounted by the census is close to the percentage of rich Americans uncounted.
(D) The number of homeless Americans is approximately equal to the number of rich Americans.
(E) The primary purpose of the census is to analyze the economic status of the American population.

不明白为什么选C

edwardbella

谢谢 受益匪浅

曳烛

Try this question:

The U.S. census is not perfect: thousands of Americans probably go uncounted. However, the basic statistical portrait of the nation painted by the census is accurate. Certainly some of the poor go uncounted, particularly the homeless; but some of the rich go uncounted as well, because they are often abroad or traveling between one residence and another.

Which of the following is an assumption on which the argument above depends?

(A) Both the rich and the poor have personal and economic reasons to avoid being counted by the census.
(B) All Americans may reasonably be classified as either poor or rich.
(C) The percentage of poor Americans uncounted by the census is close to the percentage of rich Americans uncounted.
(D) The number of homeless Americans is approximately equal to the number of rich Americans.
(E) The primary purpose of the census is to analyze the economic status of the American population.

-- by 会员 sdcar2010 (2011/6/28 20:58:35)

SDCAR2010大牛。。。我一直认为这个题出的有问题。。。就像你在52楼说的“The basic statistical portrait might mean a statistical trend, a statistical discription, a statistical map.”又或是在28楼赞同“I guess the "the basic statistical portrait" means the proportion of each group to the entire population, or something close...”的一样，我们假设这个basic statistical portrait意味着the proportion of each group to the entire population。但是如果B选项不成立的话，很明显我可以吧美国人分成the richest、the rich、the average、the poor、the poorest.(就像OG的诊断性测设那样分类一样）那很明显无论怎样，少计算the poorest或是the richest都会减少他们的比例而增加其他的。但如果B成立只分成poor和rich的话（其实这在现实中很难的），那么即使C成立了也不对。比如正常rich60%，poor40%。现在各少算10%，then what we will get？rich=50/(50+30)=62.5%,poor=30/(50+30)=37.5%!更何况这是在BC同时成立的条件下（事实上没有BC同时成立这个选项)

曳烛

哦，再问一下，为什么E不对？如果E不对的话（就是说这个分析的不是美国人口的经济状况）那么假如分析的是人口总量亦或是人口数量分布，那么很明显作者的argument跑题了。。。（也就是不成立）

sdcar2010

比如正常rich60%，poor40%。现在各少算10%，then what we will get？

Your calculation is wrong.  ercentage and Number. What C says is that the percentage of poor Americans uncounted by the census is close to the percentage of rich Americans uncounted. That means:

Before: Rich 60%; Poor 40%
10% error (remember, 10% is a RELATIVE term, not an ABSOLUTE number!)
Now: Rich 54%; Poor 36% (Not 50% vs 30%!)