mathpermutuation
posted by sarah .
a four digit serial number
needs to be created using
digits 09. first digit is
even , no digit is repeated ,
last digit is odd

First digit is even: 4 choices (assuming zero is excluded)
Last digit is odd: 5 choices
Eight digits remain for the second digit, and 7 for the third (no repetition).
Total=product of all four numbers.