1. The problem statement, all variables and given/known data Hi So the problem in combinations is the following: In how many ways can you choose 2 letters from the following 6 letters (A,B,C,D,E,F) This is a question in combinations so I know the order does not matter, so AB is the same as BA. I use the equation (n,r) = n!/((n-r)!*r!) = 15 (See my drawing) The problem is this: If i draw out the possible combinations and add them together i get 21! What is the correct answer 15 or 21, and why?