数学T paper 2讨论专区

Razor_1130

(x-y)（dy/dx) = 4x

differential equation homogenous equation
拜托了~~

blazex

Ia large factory with many workers, 30% of the workers belong to Union A , 60% Union B and the remaining 10% does not join any union . A sample of 5 workers is selected.
1)Find the probability that the  sample has less than 2 members of Union A .
2)It is found that exactly 4 of these workers are members of unions. What is the probability that more of the members come from  
   Union A than Union B .

peaceboy

Ia large factory with many workers, 30% of the workers belong to Union A , 60% Union B and the remai ...
blazex 发表于 31-7-2010 08:30 AM

   
Ia large factory with many workers, 30% of the workers belong to Union A , 60% Union B and the remaining 10% does not join any union . A sample of 5 workers is selected.
1)Find the probability that the  sample has less than 2 members of Union A .

P(A) = 0.3

5C0 (0.3)^0 (0.7)^5 + 5C1 (0.3)^1 (0.7)^4 =0.52822


2)It is found that exactly 4 of these workers are members of unions. What is the probability that more of the members come from  
   Union A than Union B .

P(Al U ) = 0.3/0.9 = 3/9
4C3 (3/9)^3 (6/9)^1 + 4C4 (3/9)^4 = 1/9

不肯定对不对

数学系

To #323

Let
A = workers union A
B = workers union B
C = workers neither A nor B

Assume that A, B, and C are mutually exclusive.

a)  P(the sample has less than 2 workers of Union A)
= P(A=0) + P(A=1)
= 5C0(0.3)^0(0.7)^5 + 5C1(0.3)^1(0.7)^4
= 0.52822 = 0.5282(4 sf)

b) P(exactly 4 members of Unions) = 5C4(0.9)^4(0.1) = 0.32805

Thus, P(member Union A more than members Union B| exactly 4 members)
= 0.1[4C4(0.3)^4(0.6)^0+4C3(0.3)^3(0.6)^1]/0.32805
= 0.00729/0.32805 = 1/45

数学系

To #322

(x - y)dy/dx = 4x

This homogeneous differential equation is inseparable; thus the traditional integration technique is not applicable. It is also not nonhomogeneous, and we cannot apply the technique of integrating factor. I guess some substitution is needed, is the question suggesting any dummy substitution?

Razor_1130

我也是觉得是有其他substition可是我不懂可以SUBSTITUTE什么进去

whyyie

回复 327# Razor_1130

Substitute y = vx

Razor_1130

不如你试看用 y=vx来solve...
做到了就成了unseperable。。。可能我们功夫未到家

whyyie

回复 329# Razor_1130

完整的问题和答案是什么? 不肯定自己的答案...

Razor_1130

现在没有。。可以让我看看你的方法嘛？
信息我

walrein_lim88

(x-y)（dy/dx) = 4x

differential equation homogenous equation
拜托了~~
Razor_1130 发表于 29-7-2010 07:26 PM

file:///C:/DOCUME%7E1/ADMINI%7E1/LOCALS%7E1/Temp/moz-screenshot-2.png
很久没来这里了。。
这题。。。maths T学生不需要会也无所谓啦。。。有点点牵涉到further maths T的integration了。。。
file:///C:/DOCUME%7E1/ADMINI%7E1/LOCALS%7E1/Temp/moz-screenshot-3.png

数学系

回复 332# walrein_lim88


   Great!

walrein_lim88

回复  walrein_lim88


   Great!
数学系 发表于 1-8-2010 09:52 PM

    哈哈。。。还好啦～
你现在读数学系是不是？

Allmaths

回复 332# walrein_lim88


   还是walrein 强...

数学系

回复 334# walrein_lim88


   我在申请美国研究院。

数学系

回复 334# walrein_lim88


   那你呢？stpm 吗？

walrein_lim88

回复  walrein_lim88


   那你呢？stpm 吗？
数学系 发表于 1-8-2010 11:29 PM

刚刚读大学罢了。。。
哇。。数学系。。好羡慕你哦。。现在又申请研究院。。祝你成功^^

数学系

回复 338# walrein_lim88


哈哈，也没什么好羡慕的。当你四周围的同学都是ASEAN top scholars时，那种竞争压力就大了。
你也要加油！

Razor_1130

很久没来这里了。。
这题。。。maths T学生不需要会也无所谓啦。。。有点点牵涉到further maths T ...
walrein_lim88 发表于 1-8-2010 09:45 PM

    好强。。要时间消化。。
先谢谢你哦

如你所说。。不是math t standard我放心多了

數學神童

instant coffee comes in packets of mean m g with standard deviation 1.5g. If 30 packets of instant coffee are taken and the probability that their total weight is between 370g and 380g is to be 0.05, what should be the range of m?
answer: 12.3<=m <=12.7

how to do? can anyone show working to me?