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#26 2013-03-23 21:51:19

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 104,183

Re: probability question help me

Look at the formula for no one getting drunk. The (k-1)! is the number of them.

Now if you tell me what you are trying to do I can suggest a good means of computing the numbers.

Last edited by bobbym (2013-03-23 22:33:11)

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
A number by itself is useful, but it is far more useful to know how accurate or certain that number is.

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#27 2013-03-23 23:13:58

NobodyButYou
Member
Registered: 2013-03-23
Posts: 8

Re: probability question help me

I am trying to understand the logic behind the terms that's all.

Summation from j= 0 to n of (-1)^j/j! in the numerator is not getting into my head.

As far as my understanding goes, it computes the number of ways you can give out n names to n people without any of them having their own name.

Why do we need to multiply the summation in the numerator with P(no one getting drunk)?

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#28 2013-03-23 23:21:29

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 104,183

Re: probability question help me

All the forms there were obtained empirically. By looking at the data. There just was no other way that I could solve the problem,

As far as my understanding goes, it computes the number of ways you can give out n names to n people without any of them having their own name.

That is the number of derangements which is always an integer. Your sum there is not always an integer.

Last edited by bobbym (2013-03-24 01:21:52)

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
A number by itself is useful, but it is far more useful to know how accurate or certain that number is.

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#29 2016-03-21 17:23:06

ernchung
Member
Registered: 2016-02-26
Posts: 14

Re: probability question help me

k stands for the total no. of players , how about n?

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#30 2016-03-21 17:36:49

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 104,183

Re: probability question help me

Almost a month has gone by, you will have to refresh my memory. What is your question?

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
A number by itself is useful, but it is far more useful to know how accurate or certain that number is.

Offline

#31 2016-03-22 04:04:54

ernchung
Member
Registered: 2016-02-26
Posts: 14

Re: probability question help me

the general formula of the expected value in part b, u show a lot of summations in the formula, k is the total number of players, j is a dummy , how about n?

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#32 2016-03-22 06:24:46

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 104,183

Re: probability question help me

n is the counting variable and the sum adds probabilities up for each player.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
A number by itself is useful, but it is far more useful to know how accurate or certain that number is.

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#33 2016-03-22 08:22:20

ernchung
Member
Registered: 2016-02-26
Posts: 14

Re: probability question help me

ic, i cant find the expected value for n=100 with my scientific calculator, can u gimme a hand? ty very much

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#34 2016-03-22 10:25:13

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 104,183

Re: probability question help me

Do you mean k = 100 , not n.

I will get it for you, in the meantime to check what did you get for 10?

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
A number by itself is useful, but it is far more useful to know how accurate or certain that number is.

Offline

#35 2016-03-22 10:27:37

ernchung
Member
Registered: 2016-02-26
Posts: 14

Re: probability question help me

thank you i have to hand it in 1 hour later, i should ask you earlier. i got 3.5500 for k=10

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#36 2016-03-22 10:58:35

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 104,183

Re: probability question help me

Hi;

That checks with what I got for 10. For 100, I am getting 48.505

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
A number by itself is useful, but it is far more useful to know how accurate or certain that number is.

Offline

#37 2016-03-22 11:04:51

ernchung
Member
Registered: 2016-02-26
Posts: 14

Re: probability question help me

Thank you~
I am re calculating it right now.
By the way, just want to know if you have learnt survival model before?

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#38 2016-03-22 11:07:13

ernchung
Member
Registered: 2016-02-26
Posts: 14

Re: probability question help me

I would also like to know which software or calculator are you using for these questions

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#39 2016-03-22 11:09:56

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 104,183

Re: probability question help me

I am using a CAS ( Computer Algebra System ), I like Mathematica. It is not free but many universities supply it to their students. Also, there is a version of it online. There are also free ones too.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
A number by itself is useful, but it is far more useful to know how accurate or certain that number is.

Offline

#40 2016-03-22 11:39:53

ernchung
Member
Registered: 2016-02-26
Posts: 14

Re: probability question help me

ok i will try it out later, have to work on the mid term exams today.

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#41 2016-03-22 12:33:07

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 104,183

Re: probability question help me

Ask if you need help.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
A number by itself is useful, but it is far more useful to know how accurate or certain that number is.

Offline