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大全5-19,为何选A?望NN指教

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楼主
发表于 2008-8-9 17:41:00 | 只看该作者

大全5-19,为何选A?望NN指教

19.   Recent estimates predict that between 1982 and 1995 the greatest increase in the number of people employed will be in the category of low-paying service occupations. This category, however, will not increase its share of total employment, whereas the category of high-paying service occupations will increase its share.

If the estimates above are accurate, which of the following conclusions can be drawn?

(A) In 1982 more people were working in low-paying service occupations than were working in high-paying service occupations.

(B) In 1995 more people will be working in high-paying service occupations than will be working in low-paying service occupations.

(C) Nonservice occupations will account for the same share of total employment in 1995 as in 1982.

(D) Many of the people who were working in low-paying service occupations in 1982 will be working in high-paying service occupations by 1995.A

(E) The rate of growth for low-paying service occupations will be greater than the overall rate of employment growth between 1982 and 1995.

沙发
发表于 2008-8-9 18:26:00 | 只看该作者
我怎么觉得是E啊
板凳
发表于 2008-8-9 19:01:00 | 只看该作者

这道题选项A是题目成立的必要而非充分条件。我们可以假设如果high occupation与low occupation都占50%时,比如以总数100人为例,各50人,low每增加一定数量时,只有high增加相同的数量才能使low占总数的份额不增加,如low增加10人,high必须也增加10人才可以使百分比都保持在50%,然而这是不可能的,因为题中说the greatest increase in the number of people employed will be in the category of low-paying service occupations,这说明low增加的人数要多于high,所以在各50人的情况下low的百分比(share)必然增加,与原题矛盾,所以各50人的情况不成立,而如果low小于50,high大于50的情况就更不成立,你可以自己试试。

也就是说如果题目成立,那么它必包含于A的范围内,但是A的范围并不仅仅有题目中所说的This category, however, will not increase its share of total employment, whereas the category of high-paying service occupations will increase its share这一情况,不知道你明白了吗

地板
 楼主| 发表于 2008-8-9 20:28:00 | 只看该作者

“也就是说如果题目成立,那么它必包含于A的范围内,但是A的范围并不仅仅有题目中所说的This category, however, will not increase its share of total employment, whereas the category of high-paying service occupations will increase its share这一情况,不知道你明白了吗”

就是这块不懂,请再讲讲,多谢

5#
发表于 2008-8-9 22:05:00 | 只看该作者

如果题目所说的成立,那么A肯定成立,但是根据A却不一定能推出题目中的条件:This category, however, will not increase its share of total employment, whereas the category of high-paying service occupations will increase its share.

比如,low为60,high为40,low增加了15(greatest),high增加了5,总数变为120,但low的share从原来的60%变为了62.5%,还是增加了。当然这一点不用多想,只要知道A是题目成立的必要条件即可。

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