Question

A social security number consists of nine digits in a particular​ order, and repetition of digits is allowed. after seeing the last four digits printed on a​ receipt, if you randomly select the other​ digits, what is the probability of getting the correct social security number of the person who was given the​ receipt?

Answer 1

In this case, the social security number is 9 digit but you already know the first 4 digit. That means the number you need to guess only 5 digits left. The digit is repeatable. Assuming the digits is 0-9 which was 10 digit variation, the calculation would be:

1/ (10* 10* 10 * 10 * 10) = 1/(10^5)= 1 / 100,000