Question: What is the total number of possible combinations of a nine digit number (ie., social security number) including repeating numbers?

Hi Ryan.

Since the value of one digit doesn't affect the value of the other digits, you can simply multiply the number of possibilities for each digit together. That is, if there are ten possible digits for each of nine positions, then that is

10 10 10 ... 10 (nine times).

For example, a three digit number can have 1000 possible values.

If you are actually thinking of Social Security numbers then it's not that simple. Look at

www.searchbug.com/peoplefinder/invalid-social-security-numbers.aspx

Hope this helps,
Stephen and Penny