求助。。。。。。。。

Spencer125 · 发表于 2013-10-13 23:55:05

3. Currently people in the United States eat, on the average, 1,431 pounds of food per year, 35 pounds more than in 1980. This increase is, at least in part, because people between the ages of 15 and 64 have accounted for an increasing share of the population.
Which of the following can be properly inferred from the passage above?
(A) More than half of the current population of the United States is between the ages of 15 and 64.
(B) The population has risen since 1980.
(C) Children below the age of 15 require, on the average, more food than do people over the age of 64.
(D) Before 1980 children below the age of 15 outnumbered people between the ages of 15 and 64.
(E) Individuals between the ages of 15 and 64 consume, on the average, more food than do those younger or older.
答案是E
我不明白的是，现在比80年多了35KG而且文中说因为15到64的人的比例变大了，怎么会得出E的结论？消耗量的增长不是因为人口数量的增长么？怎么可以得出那个群体对事物的消耗比另外的群体大？
还是我理解错了？求助NN

Spencer125 · 发表于 2013-10-14 10:40:46

uppppppppppppppppppp

elainecao · 发表于 2013-10-14 11:16:01

可以从加权平均的角度去理解:
average comsumption per year=15~64岁人的比例*15~64岁人的average consumption+其他年龄段的比列*其他年龄段的average consumption；
原文逻辑链是：15~64岁人的比例↑=>average comsumption per year↑
那么结合上式就可以推出15~64岁人的average consumption>其他年龄段的average consumption

Spencer125 · 发表于 2013-10-14 11:42:33

elainecao 发表于 2013-10-14 11:16
可以从加权平均的角度去理解:
average comsumption per year=15~64岁人的比例*15~64岁人的average consumpt ...

但如果要使得等式左面的average comsumption per year 增加，等式右面不一定可以推出15~64岁人的average consumption>其他年龄段的average consumption。或者15~64岁人的average consumption下降，但其他年龄段的average consumption上升的更快。同样可以满足条件呀？

elainecao · 发表于 2013-10-14 13:46:37

就算真如你所说的“15~64岁人的average consumption下降，但其他年龄段的average consumption上升的更快”，还是满足“15~64岁人的average consumption>其他年龄段的average consumption”这样的条件的。。。你说的只是个可能的过程，这个不等式说的是必然的结果。。。

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