This is a problem about combinations where the order doesn't matter. The solution is usually written as 7C2 (seven choose two) and has the value
[tex]\frac{7!}{(7-2)!2!}=21[/tex]Comment: 7C2 is the answer to the question "How many pairs (in our case, these pairs are seen as games played) can we form from a group of 7 things?".
