弱弱的小问GWD-29-35~~拜托各位大侠。。

ore612

In Patton City, days are categorized as having heavy rainfall (more than two inches), moderate rainfall (more than one inch, but no more than two inches), light rainfall (at least a trace, but no more than one inch), or no rainfall.  In 1990, there were fewer days with light rainfall than in 1910 and fewer with moderate rainfall, yet total rainfall for the year was 20 percent higher in 1990 than in 1910.

 

If the statements above are true, then it is also possible that in Patton City

 

1. the number of days with heavy rainfall was lower in 1990 than in 1910

2. the number of days with some rainfall, but no more than two inches, was the same in 1990 as in 1910

3. the number of days with some rainfall, but no more than two inches, was higher in 1990 than in 1910

4. the total number of inches of rain that fell on days with moderate rainfall in 1990 was more than twice what it had been in 1910

5. the average amount of rainfall per month was lower in 1990 than in 1910

答案怎么是A呢。。  light rainfall he moderate rainfall 不是都是less than 1910吗？ total higher than....怎么会heavy rainfall 还少呢 

deadknot

就是啊，都说了中等降雨和少量降雨的日子少比1910少了。。。晕哦！

hughlv

请看下面的详细解释。

A.the number of days with heavy rainfall was lower in 1990 than in 1910

这个可能性是存在的。稍后解释。

B.the number of days with some rainfall, but no more than two inches, was the same in 1990 as in 1910

这里指两种降雨量的天数之和：moderate rainfall以及light rainfall。因为题干中很明白提到In 1990, there were fewer days with light rainfall than in 1910 and fewer with moderate rainfall。各自都少于1910，因此1990的两种降雨量的天数之和是少于1910对应的天数。可以推断出B和C均不成立。

C.the number of days with some rainfall, but no more than two inches, was higher in 1990 than in 1910

同B的解释。排除C。

D.the total number of inches of rain that fell on days with moderate rainfall in 1990 was more than twice what it had been in 1910

从B的解释可知：1990年的moderate rainfall天数(m)低于1910年对应的天数(n)。这个选项研究的是moderate rainfall所产生的总降雨量。因为moderate rainfall每天的最低降雨量要大于one inch，并低于或等于two inches，所以1990年所对应的总降雨量最低要大于m x 1 (inch) = m (inches)，最大不超过m x 2 (inches) = 2m (inches), 用数学开闭区别表示为（m, 2m]。同理1910年对应的总降雨量范围为 (n, 2n]。因为m < n，所以2m < 2n，及1990年moderate rainfall的最大理论降雨量2m肯定小于1910年moderate rainfall的最小理论降雨量n的2倍。

通过这番推导，可以得出选项D不可能成立。

E.the average amount of rainfall per month was lower in 1990 than in 1910

这个比较好排除，因为total rainfall for the year was 20 percent higher in 1990 than in 1910，所以平均到每个月也会是20 percent higher in 1990 than in 1910。选项E也不成立，排除之。

终于可以回到选项A了。为什么我说它有可能成立呢？主要是heavy rainfall的范围是没有上限的，给了人无限的发涌占洹４犹飧晌颐强梢缘贸?990年的heavy rainfall对应的total rainfall肯定要高于1910年对应的total rainfall（而且是至少高20%）。但这个真是跟天数没有关系，举个简单的例子，如果1990年下的是暴雨每天都是1000inches，而1910年时都是中规中矩大雨每次3inches，这样算很容易的就可以得知A成立是完全有可能的。

[此贴子已经被作者于2009/8/3 16:32:28编辑过]

ore612

懂啦~~~非常感谢大牛同志！！！！    祝(⊙o⊙)你幸福~~

独眼豆豆

我是来顶3楼的。。

虽然明白了AD，但是现在是第一次明白为什么BC不对，都不知道some rainfall是什么东东。。

谢谢大牛

gmatwc

some rainfall, but no more than two inches

applehao

这道题我是这样做的,先列表,

	rainfall days
year	1990	1910
H(>2)	X天	A天
M(1<M<=2)	Y天	B天	Y<B
L(0<L<=1)	Z天	C天	Z<C

设1990年的M rainfall days为X天，1910年的为B天，根据题干信息有X<B。设1990年的L rainfall days为Z天，1910年的为C天，有Z<C。题干告知1990年的rainfall总量比1910年高20%，则有可能XH>AH,或YM>BM，或ZL>CL。因此可以很容易将BCE排除掉。

关于D选项的排除我是这样考虑的。D选项说YM twice more than BM。根据题干已知Y<B，而M作为变量，取值范围从大于1到小于等于2，显然最大值不到最小值的两倍，所以YM不可能是BM的两倍以上。D不成立。只剩A选项。即便X<A，但H的取值范围很广，XH>AH的可能性很大。

peiswanho

推呀

一目了然!!!