# Probability : Counting Principle

A social security number has 9 digits. How many different S.S numbers are possible if:

a. repetition of digits is permitted

b. repetition of digits is not permitted

c. the first digit cannot be a 0 and repetition is not permitted

I need the layout (counting principle)

ex. 9 8 7 - 6 5 - 2 1 4 3

- - - - - - - - -

Thankyou

I think the answer for a= 1,000,000,000

for b= 3,628, 800 and for c= 3,265,920

Let me know!

https://brainmass.com/math/probability/probability-counting-principle-10168

#### Solution Preview

It's a counting problem. Follow the condition carefully and you won't miss it.

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A social security number has 9 digits. How many different S.S numbers are possible if:

a. repetition of digits is permitted

b. repetition of digits is not permitted

c. the first digit cannot be a 0 and repetition is not permitted

I need the layout(counting principle)

ex. 9 8 7 - 6 5 - 2 1 4 3

- - - - - - - - -

Thankyou

I think the answer for a= 1,000,000,000

for b= 3,628, 800 and for c= ...

#### Solution Summary

Counting problems are solved and explained.