想问个数学题

chasemer

In a demographic study, the population and total income of a certain region were estimated from other data, and both estimates had lower and upper limits.  At the time of the estimates, was the per capita income for the region greater than $16,500?

(1)   The lower limit for the estimate of the population was 330,000 people.

(2) The lower limit for the estimate of the total income was $5,500,000,000.

答案说选E啊,可我觉得是C啊.因为如果都有上下限的话,比如a<x<b,c<y<d,a,b,c,d都是大于0的,那不是应该 a/c<x/y<b/d 吗?那如果两个下限是330000和5500000000的话,应该只要5500000000/330000=16667吧.

是不是我弄错了...

chasemer

还有一个,

If x ≠ 0, then (x + 1/x)² - (x - 1/x)² =

 

 

A.    1/x

B.    x

C.    1

D.    2

E.    4

 

这里应该是没答案的吧,不是应该是4/x么...

liushuixian

第一题如果条件（１）说的是The higher limit for the estimate of the population was 330,000 people, 因为要保证分母最大，分子最小才使得分数值最小．

第二题是x和x的倒数相加的平方　减去　x和x的倒数相减的平方　

你把题看错啦