十月梦队数学讨论专帖，请NN多多支持！！

joice

I am thinking postpond to the end of OCT, because i am still in OG SC..
Can't you take the test in HanZhou? It looks you have school in Hanzhou.

Are you ready? You are a small hard-working bee.

祈晴坊主

以下是引用joice在2003-9-26 21:40:00的发言：
I am thinking postpond to the end of OCT, because i am still in OG SC..
Can't you take the test in HanZhou? It looks you have school in Hanzhou.

Are you ready? You are a small hard-working bee.

yeah, i am a hangzhou native ,and have my collage education in hangzhou too

hehe  

i've determined my mind to crack it in the middle of OCT
cos i no longer want to hold it

as s senior student ,i find studying is becoming boring and boring ~~~~~~~~~
i don't have any patience to stand it

hehe ,get tied of the study,worn out~~~~~~~~~~~

anyway,for the last two weeks ,i would stick to it

haha haha

i am a happy small bee, working along the flower~~~~

taste around the sweet ~~~~

i am a happy small bee,full of strength

cos i ate so so much ferrero chocolate last night~~~

祈晴坊主

九月剩下的几道题请教

253). 正态分布，落在正负一个标准方差(d)内概率68％，问正两个d的概率。 68%+(1-68%)/2

这道题目什么意思，如果按照作者的表述，求两个方差的概率的话，这种做法是错的吧

271). 有个方差的问题，A,B两个数列，问A的方差大于B吗 1， A的算术平均数>B,  2， A的中数>B,
参考答案：: D   思路: 该题心里没有底。

这题应该是E吧

290)、(a,b)是x+y=4上的点，问(a,b)是否在第一象限： (1)y>2  (2)x>0 答案：B

这题应该是C吧

joice

253). 正态分布，落在正负一个标准方差(d)内概率68％，问正两个d的概率。 68%+(1-68%)/2

I am not really understand the question. if the question is to find the probability when SD =+2, then i think the answer is wrong. Let me try :
in z score, 95.44% of the area is within 2 standard deviations,
1- .9544 = . 0456
.5 - .0456 = .4544
so the probability is 45.44%

Please let me know, if i did it wrong.

祈晴坊主

以下是引用joice在2003-9-30 21:48:00的发言：
253). 正态分布，落在正负一个标准方差(d)内概率68％，问正两个d的概率。 68%+(1-68%)/2

I am not really understand the question. if the question is to find the probability when SD =+2, then i think the answer is wrong. Let me try :
in z score, 95.44% of the area is within 2 standard deviations,
1- .9544 = . 0456
.5 - .0456 = .4544
so the probability is 45.44%

Please let me know, if i did it wrong.

如果按照以前背过的话
N（2）是95。45
N（3）是96。73

但是如果按题目的意思，怎么推
我觉得它是错的

hz

253、如果mean是M，从答案倒推，题目应该问的是小于M+d的数的概率，或者是大于M-d的数的概率。

joice

If it is: 问正两个d的概率, 题目应该问M+d的数的概率?
           问negative 两个d的概 率,  是大于M-d的数的概率?

[此贴子已经被作者于2003-9-30 22:52:55编辑过]

hz

好象不能这么理解，这只是根据答案倒推的。只能说题目中未把问题表述清楚。

joice

thanks数学老师. your neck is fine, right?

hz

I'm fine. Thank you! And how about your eyes?