could you please clarify why we don't count 2 "s" of "password" and use n=7 instead of n=8 ?

Hey Amir, Thank you for your question! The reason we don't consider the letter 's' twice is because it doesn't matter whether we take the first S in the word PASSWORD, or the second S - these letters are identical. Therefore, we only need to identify the unique letters in the word PASSWORD which would form the set of possible letters for the code. Hope that helps! Kind regards, 365 Hristina