A social security number consists of nine digits between 0 t

A social security number consists of nine digits (between 0 to 9 inclusive) in a particular order, and repitition of digits allowed.

A. How many different social security numbers exsist?

B. What is the probability that if randomly selecting digits you get the social security number of the president?

C. If repitition of digits is not allowed in a social security number, then how many social security numbers would exsist?

Solution

A)

There are 10 digits 10 choose from 0 to 9. As there are 9 digits, there are 10^9 = 1,000,000,000 numbers. [ANSWER]

b)

The president only has 1 socia security number. Thus,

P = 1/(10^9) = 0.000 000 001 [ANSWER]

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c)

If there are no repetition of digits, then there would be 10P9 = 3628800 numbers. [ANSWER]