Question 729775
There are 7 possibilities for the first digit. <P>
Since digits cannot repeat, there are 10-1 possibilities for the second digit (you've already used one for the first digit).<P>
There are 10-2 possibilities for the 3rd digit.<P>
There are 10-3 possibilities for the 4th digit.<P>
7*9*8*7 = 3528 possible pass codes.