A password consists of four different letters of the alphabet. How many different possible passwords are there?

Six with two left over if I am not mistaking?

26 letter in alphabet

several scenarios

1. can repeat and only lowercase

26^4 or 456976 ways

2. can repeat and lower and uppercase

26^4*2^4 or 7311616 ways

3. cannot repeat and only lowercase

26*25*24*23 or 358800 ways

4. cannot repeat and lowercase and uppercase

26*25*24*23*2^4 or 5740800 ways