I hope this is the right place to put this thread.
How many combinations of three letters taken from the letters A,A,B,B,C,C,D are there?
I take it as but the answer is 13.
Thanks for any help.
Hello, arze!
Your answer would be correct if there were 7 different letters.How many combinations of three letters taken from the letters A,A,B,B,C,C,D are there?
Because of the duplicated letters, I counted the cases rather primitively.
How many 3-letter combinations have 3 different letters?
There are 4 different letters available, and we pick 3 of them.
. . There are: . combinations.
How many 3-letter combinations have 2 of one letter and 1 other letter?
There 3 choices for the pair (A, B, or C).
Then there are 3 choices for the single letter.
. . There are: . combinations.
Therefore, there are: . possible combinations.