Expert: Steve Holleran - 9/7/2007

Question
I am an adult, this is not a homework question but is a math question. I was thinking of this myself and did not read this question anywhere. If there are only 9 numbers for social security numbers, and millions of people who have social security numbers, how many different sequences of numbers can be made from just 9 numbers? And what would be the system to figure out how many  sequenced numbers can be gotten from 9 numbers. Very curious. Thank you, Todd

Answer
Hi Todd,

Okay, if you allow that digits can be repeated, that is, maybe someone has the SSN 888-88-8888, then for each digit in the number there are 10 possibilities.

So, there are 10*10*10 - 10*10 - 10*10*10*10 =  10^9
or 1 billion possible SSN's.  Seeing as we have only 300 million people, it looks like there's plenty to spare!

Steve Holleran