Question

A 2 letter password from the letters A, B, C, D, E, and F. The password cannot have the same letter repeated in it. How many such passwords are possible?

Answer 1

I tryed to write out all of the combinations, but it wouldn't let me.
Each letter has 5 ways to write it and there are 6 letters. Multiply these two numbers.
So, in all there are 30 different combinations.

Answer 2

5 ways to select the 1st letter
4 ways to select the 2nd letter
3 ways to select the 3rd letter
2 ways to select the 4th letter

-------------
Total # of ways = 5*4*3*2 = 120 passwords
----------------------
Another way to get the answer 5P4 = 5!/(5-4)!