Combinatorics: how many different triples of cards can be formed let's say i have a hand of cards.
the number of cards i have in my hand is x > 3.
how many unordered different triples of cards can i form with the cards in my hand?
example:
i have the following cards in my hand: A B C D
i could form 
A B C
A B D
A C D
B C D
4 different triples can be formed.
i am looking for a formular that gives me the number of triples depending on x.

You have $x$ possibilities to choose the first card, $x-1$ for choosing the second one and $x-2$ for choosing the third one. If you multiply these numbers, you get $x(x-1)(x-2)$. However, as you look for unoredered triples, you have to divide this by the number of all possible ordering of 3 cards, which is $3!$ and you get
$$\frac{x(x-1)(x-2)}6.$$
Nothe that this is the same as $\binom x3$, what is exactly what you would expect. See http://en.wikipedia.org/wiki/Combination
