All the question is in the title:
How many 2-tuple can I form from the elements of a n-tuple
Supposing all elements are differents also (eg: (A,C,D,I,X,Y))
is it simply $\binom{n}{2}$ ?
All the question is in the title:
How many 2-tuple can I form from the elements of a n-tuple
Supposing all elements are differents also (eg: (A,C,D,I,X,Y))
is it simply $\binom{n}{2}$ ?
If you are looking for subsets of size 2, it's $n\choose 2$. If you want ordered pairs of size 2, there are twice as many of these, so it's $n(n-1) = 2{n\choose 2}$.