Question

Mike is choosing a 3 letter password from letters A,B,C,D and E. The password cant have the same letter repeated. How many passwords are possible?

Answer 1

Remark
This problem just uses the counting principle. You have Five Letters to choose from. If you take one, 4 are left. When one of the 4 is chosen, you have three.
Your last choice is 1 of three.

Solution
5 * 4 * 3 = 60

Comment
The answer is that he can make up 60 possible passwords.