求救！OG 12-71题 A ,B 选项

璐璐Grace

Roland: The alarming fact is that 90 percent of the people in this country now report that they know someone
who is unemployed.

Sharon: But a normal, moderate level of unemployment is 5 percent, with one out of 20 workers unemployed.
So at any given timeif a person knows approximately 50 workers, one or more will very likely be unemployed.

Sharon’s argument relies on the assumption that

(A) normal levels of unemployment are rarely exceeded
(B) unemployment is not normally concentrated in geographically isolated segments of the population

不太明白为什么B比A好。原文说“at any given time”,不是正好和A的意思吻合吗？

望牛牛指点~！~！

gmat新手22

这道题我可不可以这样想，这道题是假设，也就是sharon基于什么样的假设得出的结论，B选项是很好的排出了特殊情况，A更适合做一个不太明显的support？可是我还是觉得A选项作为假设也可以似的，sharon假设她提出的百分比是不能被否认的，因此都出结论。。。急求解释！！！为啥A不对呢。。？

cloudballoon

有人可以解釋一下  這兩段話的 邏輯嗎????
實在是抓不到

90%的人 會認識失業的人
失業率 只有5% 所以有人認識50個人 會有一個以上的人是失業的

怎麼算的

Heather_Lau

我理解的意思,sharon的argument要基于均匀分布才能成立,如果是concentrated in isolated segments of the population,那么就有可能某些地区5 of 1000失业,某些地区20 of 100失业(supposed).
so,既然要得出50个人中可能有至少1个unemployed就必须没有特殊情况.

sdcar2010

只要认识20个人 则就会有一个人失业?  Not always . . . Knowing 50 people would give Sheron's arugment a better chance.

wangfuxuan

S的回答中 正常失业率是5%  为什么他还说如果一个人大约认识50个人 至少有一个人失业 ， 按比例算  不是只要认识20个人 则就会有一个人失业？？？   还有 他说的话到底是支持R的话？ 还是反驳？  没看出他们两个人话有什么联系呀。。

sdcar2010

Roland hints that the unemployment rate is high since 90% people know someone is unemployed.

Sharon disagrees and claims it is normal for 90% people to know someone who is umemployed at a normal umemployment rate of 5%.

For necessary assumption questions, just use negation and see if that would cause the arugment to cumble.  If so, that answer choice is correct.  You do not need to worry why other choices are not assumptions other than that those wrong choices have no impact on the argument.

Let's negate B.
Unemployment is normally concentrated in geographically isolated segments of the population. If this is true, then certain area will have extremely high unemployment rate (let's say 10.5%) while other areas will have extremely low unemployment rate (let's say it is 0.5%). The national average for unemployment is still 5%. Then in the area with low unemployment, every 200 people will have one unemployed.  Then if one knows 50 people, it is likely that none of these 50 people are unemployed. Sharon's argument falls apart.