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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,302

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.Of course that result can be rigorously obtained, but who cares?Combinatorics is Algebra and Algebra is Combinatorics.**

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

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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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,302

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.Of course that result can be rigorously obtained, but who cares?Combinatorics is Algebra and Algebra is Combinatorics.**

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