Wednesday, January 6, 2010

How do I figure out the probability?

ok, I have 50 playing cards and 25 are dealt to one person and 25 to another, how do I make an organized list to show all the possible combinations of cards?How do I figure out the probability?
If you have n objects and chose r of them, the number of combinations is:


n! / ( r! (n-r)! )


this can be written as nCr








there are 50 C 25 = 1.264106e+14 combinations... why would you want a list of this many combinations?How do I figure out the probability?
You need to learn about combinations and permutations.


In combinatorial mathematics, a combination is an un-ordered collection of unique sizes. (An ordered collection is called a permutation.) Given S, the set of all possible unique elements, a combination is a subset of the elements of S. The order of the elements in a combination is not important (two lists with the same elements in different orders are considered to be the same combination). Also, the elements cannot be repeated in a combination (every element appears uniquely once); this is often referred to as ';without replacement/repetition';. This is because combinations are defined by the elements contained in them, thus the set {1,1,2} is the same as {2,1,1}. For example, from a 52-card deck any 5 cards can form a valid combination (a hand). The order of the cards doesn't matter and there can be no repetition of cards.








In several fields of mathematics the term permutation is used with different but closely related meanings. They all relate to the notion of mapping the elements of a set to other elements of the same set, i.e., exchanging (or ';permuting';) elements of a set.
assuming that you don't care about order (ie getting dealt the ace of spades first and the king of spades second is the same as getting the king of spades first and the ace of spades second) the number of differenct combinations would be 26 factorial

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