tania的考试复习计划贴：谢谢大家的帮助和支持！！M51,V41,760!

vacationer

问一道去年9月的机井,这个方差的东东我没学过, 一点都不会啊

27.去年9月机经,那道标准方差为68%的那道,选84%;

【2003/09   (194) mean是m,68%的数在m的方差d之内，问多少比例的数小于m+d? (3次)              参考答案:.  84%】

xdf讲义中的题目：有一个symmetric数列，mean＝m，有68%的数在标准方差d之内，问小于m+d的数占所有数的多大比例？

流沙：因为68％的在方差之内，所以小于m+d的比例是68%+(1-68%)/2=84%

AegeanSea2006

以下是引用vacationer在2005-9-14 22:55:00的发言：

问一道去年9月的机井,这个方差的东东我没学过, 一点都不会啊

27.去年9月机经,那道标准方差为68%的那道,选84%;

【2003/09   (194) mean是m,68%的数在m的方差d之内，问多少比例的数小于m+d? (3次)              参考答案:.  84%】

xdf讲义中的题目：有一个symmetric数列，mean＝m，有68%的数在标准方差d之内，问小于m+d的数占所有数的多大比例？

流沙：因为68％的在方差之内，所以小于m+d的比例是68%+(1-68%)/2=84%

Vacationer别着急，很简单的一个概念，看看我能不能给你讲明白。

方差和标准差的意义:描述一个样本和总体的波动大小的特征数.标准差大说明波动大；

我把它简化理解成数轴上分布在算术平均数m周围的点，见下图：

---。--------------。--------------。-------------->  假设这是数轴,下面标的是数轴上的点

m-d                 m                  m+d                   （d是方差）

那么题目说，68%在d之内，就是说在区间[m-d, m+d]中的数字占68％，求小余m+d的数？

看数轴我们得知，如果整个数轴是100％的话，那么大于m+d的，就有(100%-68%)/2＝16％，由此得知，小余m+d的，就是1－16％＝84％。。

完了，罗里罗嗦的，不知说明白没有，反正我又糊涂了。。。

babypace

说很明白，谢谢爱情海！我明白了。

babypace

以下是引用tania在2005-9-14 13:45:00的发言：

好奇怪，今早做了一套priceton，数学错了一个，竟然只有46，想不通！！不过是第三题，那也不至于吧！！受了点打击，没上700

不想了，先去睡一大觉，下午看gwd rc，改善一下心情！现在能看多少是多少，给自己加加油

tania 一定是750左右的分数，发挥正常就没有问题的。不要担心。这两天心情好一点，考试就当平时一个练习用的GWD。加油！

vacationer

以下是引用tania在2005-9-13 17:26:00的发言：

汇报与3w的短期讨论结果，gwd-31答案修正如下：

EDCBD  CEADA   BBD(B)AA    EBA(B)BC

BDAEE  BBEEB   EBD

现在13题和18题还没有形成共识，欢迎继续讨论！！

晕,还是好多不一样

7A, 13B, 16D,18C, 28 C

18题我刚刚觉得C不对,现在又懵了, 不知道选哪个,好像都不对

31－18: According to a recent survey of municipal services, the city’s streets could be cleaner, its fire code be better enforced, and its crime rate reduced if the current administration improved its management practices.

A: be better enforced, and its crime rate reduced

B: better enforced, and its crime rate reduced

C: could be better enforced, and it could reduce its crime rate

D: better enforced, and its crime rate could reduce

E: could be better enforced, and its crime rate reduce

[此贴子已经被作者于2005-9-15 4:32:04编辑过]

水模样

LZ加油

vacationer

以下是引用AegeanSea2006在2005-9-14 23:38:00的发言：

Vacationer别着急，很简单的一个概念，看看我能不能给你讲明白。

方差和标准差的意义:描述一个样本和总体的波动大小的特征数.标准差大说明波动大；

我把它简化理解成数轴上分布在算术平均数m周围的点，见下图：

---。--------------。--------------。-------------->  假设这是数轴,下面标的是数轴上的点

m-d                 m                  m+d                   （d是方差）

那么题目说，68%在d之内，就是说在区间[m-d, m+d]中的数字占68％，求小余m+d的数？

看数轴我们得知，如果整个数轴是100％的话，那么大于m+d的，就有(100%-68%)/2＝16％，由此得知，小余m+d的，就是1－16％＝84％。。

完了，罗里罗嗦的，不知说明白没有，反正我又糊涂了。。。

谢谢爱情海mm!

大概明白了. 那方差和标准差有什么不同呢? 都是怎么得来的?

不要笑我问的问题白痴啊

vacationer

16: In recent years, networks of fiber-optic cable have been replacing electrical wire for transmitting telecommunications signals. Signals running through fiber-optic cables deteriorate, and so the signals must be run through a piece of equipment called a regenerator before being transmitted father. Light-Line is the leading manufacturer of signal regenerators. Therefore, Light-line is one of the companies that will most benefit if new long-distance fiber-optic telecommunications networks are constructed.

Which of the following, if true, casts the most doubt on the prediction about light-ling’s prospects?

A: Telecommunications signals sent along electrical wires can travel much farther than signals transmitted through fiber-optic before needing to be regenerated.

B: Expanding its production of regenerators will require Light-line to spend proportionately more on labor and materials.

C: The volume of signals that a fiber-optic cable can carry is several thousand times greater than the volume that can be carried by an electrical wire of similar size.

D: There are technologies that enable telecommunications signals to be transmitted without either wire or fiber-optic cable.

E: Several manufacturers are developing regenerator technologies that will allow signals to be transmitted many times farther than at present before requiring regeneration.

28: Rock samples taken from the remains of an asteroid about twice the size of the 6-nuke-wide asteroid that eradicated the dinosaurs has been dated to be 3.47 billion years old and thus is evidence of the earliest known asteroid impact on Earth.

A: has been dated to be 3.47 billion years old and thus is

B: has been dated at 3.47 billion years old and thus

C: have been dated to be 3.47billion years old and thus are

D: have been dated as being 3.47 billion years old and thus

E: have been dated at 3.47 billion years old and thus are

这两题你们都达成共识了,可是我不明白

[此贴子已经被作者于2005-9-15 4:34:09编辑过]

tania

谢谢baby和vacationer的鼓励，只剩4天了，我一定会努力到底的！！

大家一起加油哦！！

tania

以下是引用vacationer在2005-9-15 3:09:00的发言：

晕,还是好多不一样

7A, 13B, 16D,18C, 28 C

18题我刚刚觉得C不对,现在又懵了, 不知道选哪个,好像都不对

31－18: According to a recent survey of municipal services, the city’s streets could be cleaner, its fire code be better enforced, and its crime rate reduced if the current administration improved its management practices.

A: be better enforced, and its crime rate reduced

B: better enforced, and its crime rate reduced

C: could be better enforced, and it could reduce its crime rate

D: better enforced, and its crime rate could reduce

E: could be better enforced, and its crime rate reduce

经查，reduce和rate的用法只能是reduce the rate，所以这里应该是rate be reduced 的用法，C之所以不对，是因为其中的it不清楚，it 不可以指代A's B中的A，而且A选项中的三个部分完美平行对称，后面两项都省略了第一项中的could be，所以应该选A。