just a question regarding passwords .computing the possibilities for a numerical PIN [closed]

How many possibilities for a numerical PIN with exactly 9 digits? How about a PIN with no more than 9 digits?

• This is a basic mathematic question. It might have been better suited on math.SE. – A. Hersean Jul 26 '19 at 14:56
• I'm voting to close this question as off-topic because it's a basic math question. – AleksanderRas Jul 27 '19 at 15:10

For a PIN of length 9, you have exactly 10^9 = 1000000000 combinations (which can be brute-forced by a computer in less than one second). That's 29.9 bits of entropy.
For a PIN of at most 9 digits, you have exactly 10^9 + 10^8 + ... + 10^1 = 1111111110 combinations, which is not that greater than the previous answer. That's 30.0 bits of entropy.