Question 626467
<pre>
"5 choose 2", or "the combinations of 5 things taken 2 at a time".  It's
combinations, not permutations because order is not considered since 
A playing B is the same thing as B playing A.

C(5,2) = {{{5!/(2!*(5-2)!)}}} = {{{5*4*3*2*1/((2*1)(3!))}}} = {{{5*4*3*2*1/((2*1)(3*2*1))}}} = 10 

The 10 games are:

1. A and B play.
2. A and C play.
3. A and D play.
4. A and E play.
5. B and C play.
6. B and D play.
7. B and E play.
8. C and D play.
9. C and E play.
10. D and E play.

 Edwin</pre>