How many six-letter passwords are there that use only lowercase letters with no letter repeated?

There are 26 letters of the alphabet
you want 6-character passwords without repetitionthe first time you pick a letter, you pick from 26 lettersthe second time you pick a letter, you pick from 25 letters (no repetitions !)the third time you pick a letter, you pick from 24 letters, and so onthe answer is 26*25*24*23*22*21=165,765,600 passwords