数学T paper 2讨论专区

peaceboy

instant coffee comes in packets of mean m g with standard deviation 1.5g. If 30 packets of instant c ...
數學神童 发表于 7-8-2010 10:17 PM

    我不懂为什么，不过你的答案好像是从 370/30 和380/30拿来的

DADDY_MUMMY

我不懂为什么，不过你的答案好像是从 370/30 和380/30拿来的
peaceboy 发表于 8-8-2010 08:59 PM

同感

blazex

1)At a tourist spot, a car hiring company has 4 cars to be hired for a day. The  
  demand by hirers in a day follows a Poisson distribution with a mean of 3 cars .  
  Find the probability that 4 cars are hired in a day.
  (The demand by hirers in a day can be more than 4 cars.)

Allmaths

1)At a tourist spot, a car hiring company has 4 cars to be hired for a day. The  
  demand by hirer ...
blazex 发表于 15-8-2010 06:05 PM

方便写下答案吗？

blazex

回复 345# Allmaths

答案是0.353

whyyie

回复 344# blazex

Let X be number of cars hired per day
X~Po (3)

P(exactly 4 cars hired per day)
= P(4 or more cars hirer per day)
= 1- P(X=0) - P (x=1) - P(x=2) - P(x=3)
= 0.353

tHunder_r@iN

这里有没有人用 pelangi text book?
我 probability差下

tHunder_r@iN

Three dice are tossed together.Find the probability that the sum of the score is 5

不懂为什么找不到答案啊!!

Allmaths

Three dice are tossed together.Find the probability that the sum of the score is 5

不懂为什么找不 ...
tHunder_r@iN 发表于 16-8-2010 06:02 PM

n(S)=6x6x6                                                                                                                          =216
Let A=probability of the sum of the score is 5

1st case=1+2+2
2nd case=1+3+1
3rd case=1+1+3
4th case=2+1+2
5th case=2+2+1
6th case=3+1+1


note:red is dice 1, blue is dice 2, green is dice 3


n(A)=6


p(A)=n(A)/n(S)
      =6/216
      =1/36

數學神童

Ali has 4 pairs of different colour socks in a drawer. He selects socks one at a time randomly from the drawer without replacement until he gets a matching pair.
a) Show that the probability that he does not have a matching pair after selecting the second sock is 6/7.
b)Find the probability that he does not have a matching pair after the fourth sock.
c) Find the probability that the first three socks include a matching pair

peaceboy

Ali has 4 pairs of different colour socks in a drawer. He selects socks one at a time randomly from  ...
數學神童 发表于 20-8-2010 10:15 PM

    1) (8/8)*(6/7)=6/7

2)(8/8)*(6/7)*(4/6)*(2/5) =0.2286

3) (8/8)(1/7) + (8/8)(6/7)(2/6)=0.4286

有答案么？probability很难确定 = =

數學神童

(8/8)(1/7) + (8/8)(6/7)(2/6)=0.4286

why 2/6?? not 1/2 meh?

peaceboy

(8/8)(1/7) + (8/8)(6/7)(2/6)=0.4286

why 2/6?? not 1/2 meh?
數學神童 发表于 21-8-2010 07:42 PM

    第三个才有一样的袜子 = (8/8)(6/7)(2/6)

如果我们有这些袜子

1 1
2 2
3 3
4 4

第一个随便拿都以一样（拿红色）

剩下
1
2 2
3 3
4 4

第二个红色以外(6/7) 拿蓝色
剩下
1
2
3 3
4 4

第三个要成功，所以要拿到红色或蓝色
所以是2/6

Lov瑜瑜4ever

A school offers Japanese and Arabic as 2 foreign languages. The probability that a student who studies Japanese also studies Arabic is 1/4 and 1/5 of the students who study Arabic also studies Japanese too. Among the students, 1/5 of them do not study any of the 2 languages. What is the probability that a student in the school studies both languages?

What is the mean of that red color sentence?

peaceboy

The probability that a student who studies Japanese also studies Arabic is 1/4 and 1/5 of the students who study Arabic also studies Japanese too.

P(A l J) = 1/4
P(J l A) = 1/5

Lov瑜瑜4ever

The probability that a student who studies Japanese also studies Arabic is 1/4 and 1/5 of the studen ...
peaceboy 发表于 22-8-2010 02:14 PM

   
要怎样看得出他是conditional event呢？
之前我把他看成P(J n A)=1/4和P(A n J)=1/5
所以看到很奇怪咯

Lov瑜瑜4ever

Bag A contains 3 red balls and 2 green balls whereas bag B contains 2 red balls and 3 green balls. 2 balls are withdrawn from bag A to be put into bag B. Then 2 balls are taken out from B to be put in bag A. What is the probability that bag A now contains 3 red balls and 2 green balls?

peaceboy

回复 357# Lov瑜瑜4ever

基本上就是句子的逻辑
如果我说一只狗是白色的几率，是多少，你会写 P（白色l 狗）
如果我说随便找一个生物，他是白色的狗的几率是多少，你会写P(白色n狗)   [准确一点的话是  P( (白色n狗) l 生物)   ]


    The probability that a student who studies Japanese also studies Arabicis 1/4


问题说一个学日语的学生，学阿拉伯语的几率是1/4
所以写P(学阿拉伯语 l学日语 ) = 1/4

而如果问题说一个学生，学日语和阿拉伯语的几率是 1/4

写P[(学阿拉伯语 n学日语) l 学生] = 1/4
不过我们知道P(学生) = 1 ( universe = 学生)  
general formula = P(学阿拉伯语 n 学日语 n 学生) /P(学生)
                         =   P(学阿拉伯语 n 学日语 n 学生)
*学阿拉伯语 , 学日语 subset of 学生

所以 =  P(学阿拉伯语 n 学日语）

解释到烂下，橙色的字可以不用看，因为属于我自己猜想的

peaceboy

Bag A contains 3 red balls and 2 green balls whereas bag B contains 2 red balls and 3 green balls. 2 ...
Lov瑜瑜4ever 发表于 22-8-2010 02:45 PM

    要用tree diagram 比较容易看

1st condition ,  take 2R from bag A
P= 3/5 * 2/4 = 3/10

so now bag B have 4R3G and bag A have 1R2G
to have 3R2G , we need to take back 2R
=4/7*3/6
=2/7

so in 1st condition . probability = 3/10 * 2/7
                                            = 3/35

2nd condition take 2G

P=2/5*1/4=1/10

so now bag B have 2R5G and bag A have 3R
to have 3R2G , we need to take back 2G

P= 5/7*4/6 = 10/21

2nd condition = 1/10*10/21 = 1/21


3rd condition , take 1R1G

P= 2/5*3/4 + 3/5*2/4
  =3/10 + 3/10
  = 3/5

so now bag B have 3R4G and bag A have 2R1G
to have 3R2G , we need to take back 1R1G

P=3/7*4/6 + 4/7*3/6
=12/21

so 3rd condition = 3/5 * 12/21
                       =12/35


so total prob  = 3/35+1/21+12/35
                    = 10/21

有点心虚，呵呵，答案对么？

tHunder_r@iN

n(S)=6x6x6                                                                                     ...
Allmaths 发表于 16-8-2010 06:44 PM

    谢谢你