Question 874151
Each password is of the form ABCD


9 choices for slot A (1-9)
10 choices for slot B (0-9)
10 choices for slot C (0-9)
10 choices for slot D (0-9)


Multiply out the number of choices: 9*10*10*10 = <font color="red">9000</font>


If repeats are allowed, then there are <font color="red">9000</font> different passwords.