Combinatorics TRUE/FALSE

**chopet** · October 12th 2007, 01:35 AM

Given 5 balls, how many ways are there to place them in 3 boxes?
(There are no limitations, i.e. one box can contain all 5, while the rest can contain none.)

Letting the number of balls be n, and the number of boxes be r,
we know the formula is ${{n+r-1} \choose n}$ .
Let's call this K(0).
Evaluating, the answer is ${7 \choose 5} \ = \ 21$

If we now include a limitation, such that there be at least 1 ball in each box,
the formula is now altered to:
${{n-1} \choose {r-1}}$ .
Let's call this K(1).

Now comes the question:
The Probability of no empty box is simply ${K(1) \over K(0)}$ .

TRUE or FALSE, anyone?

**chopet** · November 2nd 2007, 08:03 AM

For anyone who wishes to know the answer,
I posted an article on my blog on this.

At the Gates of Quant World: Analogy of binary systems in probability

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