1. A social security number has 9 digits. If numbers can be repeated and all numbers can be used, there would be 10^9 possible social security numbers. Find each of the following.
a. How many possible social security numbers are there if numbers can be repeated but 0 cannot be used for the first digit?
0 can not be used for first digit, therefore, the number of ways by which the first digit can be formed by = 9 ways
Rest of the 8 digits can be formed by 10 ways.
Combinations of digits in social security numbers are investigated.