Question 729777
Since digit one must be odd, it can only be 1,3,5,7 or 9.  That means there are 5 possible digits for the first digit.<P>
Digit two and three can be any digit from 0-9, so each one has 10 possible digits.<P>
Since digit four must be even, it can only be 0,2,4,6,8.  That's 5 possible digits for the fourth digit.<P>
Since the digits can repeat, you can multiply the number of possible digits for each place.<P>
5*10*10*5 = 2500 possible 4-digit passcodes.