Social security: find the number of possible 9-digit social security numbers if the digits may be repeated.

We are asked to determine the possible number of ways of the social security number that is 9 digits if the numbers can be repeated. In this case, using fundamental counting, there are 10 possible numbers in each digit that is from zero to nine. Thus, the number of ways is 10*10*10*10*10*10*10*10*10 equal to 1 billion ways.