How do I solve this probability question?
Consider a four character password, where each character can be an upper or lower case letter or
a digit. No character can be used more than once (no repeats).
1) How many different passwords are possible?
2) How many different passwords have the character "A" in them?
3) How many different passwords are possible if the first character must be a capital letter, the
third character must be a digit, and the fourth character must be lower case?