Wahrscheinlichkeit berechnen mit Zurücklegen ohne Berücksichtigung der Reihenfolge?
Kann mir jemand diese Formel so erklären, dass ich verstehe, wie es überhaupt zu der Formel kommt und warum sie gerade bei “mit Zurücklegen” und “Nichtberücksichtigung der Reihenfolge” verwendet wird?
(n+k-1)!/(k!*(n-1)!)
Gerne auch zu einer guten Erklärung verlinken. Danke!
with the specified formula the number of possibilities, not the probability is calculated
they are obtained with the following approach:
how she is brought, I just don’t know
Supplement:
“Reduction of the formula:
The derivation of this formula is by far not as beautiful as that of the other models and is probably nowhere in the pure math study”
https://www.massmatics.de/merkzettel/#!881:Urnenmodell_mit_Zuruecklegen_without_order
by Wikipedia:
https://de.wikipedia.org/wiki/Urnenmodell
First, let the -1 go, so replace n-1 by n, looks less complicated. And then make it clear that this is a number and not a Ws. You can get a Ws if the denominator sets this number of all possibilities and the number of you considered “cheap” or whatever in the counter.
Now, take in, you have n places you want to place k elements, of course only 1 item per place (i.e. k≤n) . For the first of the k elements you have n places, for the 2nd stay n-1, for the 3rd n-2 etc. and for the k-te n-(k-1)=n-k+1. So this is the multiplication of the numbers n-k+1 to n, or of all numbers from 1 to n (=n!), if you still share this by the product of all numbers from 1 to n-k(=(n-k)!), i.e. n!/(n-k)! If you could all distinguish the k elements and count all possible different occupancy under the occupied places, you will come to k! occupancy, as k different elements can come to the 1st place, etc. However, since you don’t want to distinguish them (order no matter), you still have to share this number, so n!/(k!*(n-k)!).
However, I must confess now, I have described drawing without laying back, which also corresponds to your formula. By laying it back, it would mean that each occupied space is free again for the reception of another element, so several elements can be placed on one place. Compare the 4 types of drawing in chapter 3, results, in https://de.wikipedia.org/wiki/Urnenmodell. There is actually everything explained exhaustively, only it needs a certain affinity for mathematical formula language.