Question

Using the letters A and B, the following two-letter code words can be formed: AA, AB, BB,Ba. Using the letters A, B, and C, how many different three-letter code words can be formed?

I know that the answer is 27 from the answer sheet, but how? Can you please list the combinations? Thanks!

Answer 1

you can make 9 different letter code

Answer 2

27

Explanation:

Make a tree-diagram for all three-letter code words starting with A. Each path from the top to the bottom contains 3 letters, which is one of the code words beginning with A. There are 9 such code words. Clearly, there are 9 code words starting with B and 9 starting with C. In all, there are 27 code words.