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I understand that there would be 1,000,000,000 possibilities for a PIN of exactly nine digits (10^9, ten being the vocabulary (0-9) and the power of nine being the length of the PIN), but what about for a pin of 9 or less digits?

I am a computer security student.

Thanks.

user6336941
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    You should be able to repeat the computation for length 1, 2, 3, ... and see a pattern pretty immediately, no? –  Sep 03 '16 at 01:43
  • I'm as confused as @T.Bongers You explain the reasoning for the answer in your question. – Carser Sep 03 '16 at 01:44
  • What does 9 digit mean? Can a 9 digit number start with a zero? Any way... if so, you want to add the number of 1 digits plus the number of 2 digits etc. – fleablood Sep 03 '16 at 03:46

1 Answers1

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you want $10+100+1000+\dots + 10^9=1111111110$

Asinomás
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