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#1 Re: Help Me ! » random draw probability » 2008-08-26 11:46:32

Yes, it just means the numbers can occur any amount of times.   Like a random number generator, same concept.  A sequence could be:

4 4 1 2 3 4 2 3 1  and so on

#2 Help Me ! » random draw probability » 2008-08-24 06:15:21

swarm
Replies: 3

(edited for clarification)

I happened upon an interesting problem, and solved it, however I believe there must be an easier way to do it.  I'll present the problem and then my solution, and maybe someone can enlighten me of a simpler way.

4 balls labeled 1,2,3,4 are in a bin, and are drawn one at a time with replacement (meaning each draw is independent and has the same possible outcomes).  When all four numbers have appeared at least once, "success" has occured.  What is the probability of success after N number of draws?  For instance, for N=4 draws it is just (1 * 3/4 * 1/2 * 1/4) . 

In other words, come up with a function that takes an integer N and returns the percentage chance that all numbers have made an appearance by draw N.

I solve this problem with a matrix A:

0  0   0   0   0
1 .25  0  0   0
0 .75 .5  0   0
0  0   .5 .75 0
0  0   0  .25 1

If you raise A to the N, and then multiply it by the vector [ 1 0 0 0 0], the resulting vector will be the probabilities to be in each state, with the final value in the vector being the "finished" state (a.k.a. all numbers have appeared).


Is there a simple way to do this problem?  It doesn't seem like it should require linear algebra.. but I haven't been able to figure out another way.

Thanks a lot!

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