1) If we have 5 letters: A, A, B, C, D, in how many ways (arrangements) can we form a 3-letter "word"? How can I calculate this? The 2 A's seem to make things very complicated...and I have no clue how to do it... It's arrangements, so I think permutation will be used. Also, there are two identical "A"s, so some arrangements will be double counted or so... Denote 1st A=A1 and 2nd A=A2 A1BC and A2BC are counted as 1 "word" because actually A1=A2 Thanks for helping!