OG12 71

vakaka

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 time if 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
(C) the number of people who each know someone who is unemployed is always higher than 90 percent of
the population
(D) Roland is not consciously distorting the statistics he presents
(E) knowledge that a personal acquaintance is unemployed
答案是B


这道题看不透：
1.知道B选项为什么对，不知道其它四个选项错的原因都是什么，请指教；
2.这两个人说的话有什么关联吗？一个反驳另一个?还是一个提起个话头，另一个发表了相关的一番言论，但是两人的话没什么逻辑关系？

zhangfan90

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 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 these wrong choices have no impact

on the argument.

hz032478

sharon是反驳roland说的话，roland觉得某种情况表明失业率很高，而sharon觉得在失业率正常的情况下，也会发生roland话中的情况

正确选项应该是sharon说的那段话的必要条件，用楼上说的“取非削弱”逐一看一下就可以选出来了

ScentyGuy

R说 90%的人认识下岗的人
S说 其实失业率只有5%， 即1/20的人下岗。所以任何一个人如果认识50个人，那么他就很有可能认识下岗的人。

此两人说话的表面逻辑是
R觉得失业的人多，S说其实不多，只要认识50个人，你就会认识下岗的人。

此题的实际逻辑是
R S相互没有关系，是相互独立的信息。进一步分析题目，R说的话与此题无关，只是一个引子

B选项说 失业没有显著的地域性差异。这是一个很重要的前提。如果假设全国失业的人全在东北，那么住在西南的人就算认识再多的人也不会认识下岗的人。
换句话说，因为b得出的结论是通过数据和概率算出来的，所以学过概率的人应该知道，概率的前提就是平均分布，如果不平均分布，概率无意义。

vakaka

"概率的前提就是平均分布，如果不平均分布，概率无意义。 "
That is useful！

vakaka

“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 these wrong choices have no impact on the argument.”——That's a useful method to me!Thanks a lot!