[求助]Help me please!

yahoo750

Recent estimates predict that between 1982 and 1995 the greatest increase in the nember of people employed will be in the category of low-paying sevice occrpations. This category, however, will nor 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 workeng in low-paying service occupations than were working in high-paying wervice occupations.
B) In 1995 more people will be working in high-paying service occupations than will be workeng 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 in1982 will be working in high-paying service occupations by 1995.
E) The rate of growth for low-paying service occupations will be greater than the overall rate of employment growth between 1982 and 1995.[em05][em05]

Peace

To Odyuibe:

Just teach fish to swim!

将这题转化成数学推导应该是比较直观一些：

设几个参数：
（1） 1982年低收入职业的人数为A1， 高收入职业人数为A2
（2） 1982年至1995年
      低收入职业增加人数为a1, 高收入职业增加人数为a2

由题意得出三条式子：
（1）the greatest increase in the number of people employed will be in the
        category of low-paying service occupations
        ==》a1>a2

（2）this category, however, will not increase its share of total employment
        ==》A1/(A1+A2) >= (A1+a1)/(A1+a1+A2+a2)

（3）whereas the category of high-paying service occupations will increase its share
        ==》A2/(A1+A2) < (A2+a2)/(A1+a1+A2+a2)

为简化（2），（3）两个式子，设
1/(A1+A2) = K   
1/(A1+a1+A2+a2) = P
（这里我要打一个伏笔：K>）

则（2）（3）两个式简化为
A1*K >= (A1+a1) * P  即  （K-P）* A1 >= P * a1  (4)
A2*K <  (A2+a2) * P   即  （K-P）* A2 < P * a2  (5)

由于 a1>a2，我们很快得出 P * a1 > P * a2

因此，从（4）（5）两个式子中，即可得出
（K-P）* A1  >=  P * a1  > P * a2  > （K-P）* A2

简化得出：（K-P）* A1 > （K-P）* A2  
刚才在上面我已证明了K>, 所以K-P>0

最后得出答案A的结论： A1 > A2
(in 1982 more people were workeng in low-paying service occupations than
were working in high-paying wervice occupations.)

其实这道题的推导并不算严密，因为只考虑了只有高收入和低收入存在的情况，但是即使考虑其它因素，例如可能有中收入存在的情况。 那们也只需再设多一个参数，按上述步骤，一样可推出A的结论， 在此就不再赘述了。

别看上述推导那么复杂，其实在草稿纸上划几下就出来了。

[此贴子已经被作者于2003-4-10 12:01:36编辑过]

oddyuibe

不是很明白，

能具体写一下怎么算嘛？

谢谢

回家过年

isuffering正确！

isuffering

I THINK IS A,
JUST TRANSFER IT TO A MATHEMTICA PROBLEM, AND YOU WILL GET THE ANSWER.

回家过年

[em08]

[此贴子已经被作者于2003-4-1 22:24:27编辑过]