SOLUTION: write down all the permutations of the set of 4 letters A,B,C,D Taking at a time 2 letters?

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Question 650801: write down all the permutations of the set of 4 letters A,B,C,D Taking at a time 2 letters?
Answer by Edwin McCravy(20054) About Me  (Show Source):
You can put this solution on YOUR website!
AB, AC, AD, BA, BC, BD, CA, CB, CD, DA, DB, DC
There are 12. That's because there are 4 ways to choose the first letter.
For each of those 4 ways to choose the first letter, there remain only 3
ways to choose the second letter (because you cannot choose the same letter
that you chose for the first letter). That's 4×3 or 12 ways, and they are
listed above.
Edwin