 #1
 409
 9
Homework Statement
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!/((nr)!*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?
Attachments

15.8 KB Views: 374