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cinar Group Title

password question, need some help..

  • one year ago
  • one year ago

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  1. cinar Group Title
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    • one year ago
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  2. lopus Group Title
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    http://www.khanacademy.org/math/probability/v/probability-using-combinations

    • one year ago
  3. wio Group Title
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    a) Let's try first by calculating the total number of passwords without requirements, and then subtracting the total number of passwords which DON'T meet the requirements.

    • one year ago
  4. wio Group Title
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    Cinar, can you do this?

    • one year ago
  5. cinar Group Title
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    62^10

    • one year ago
  6. cinar Group Title
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    that is total only..

    • one year ago
  7. wio Group Title
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    Now how many don't meet the 'at least one digit' rule, how many don't meet the 'at least one lower case letter', and how many don't meet the 'at least one upper case letter' requirement?

    • one year ago
  8. cinar Group Title
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    10^52+10^36+10^36

    • one year ago
  9. cinar Group Title
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    listen I'll be right back ok, give me couple minutes, I need to do something..

    • one year ago
  10. wio Group Title
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    \( (26 +26)^{10}\) Have no digit \( (26+10)^{10} \) Have no lower case \((26+10)^{10} \) Have no upper case

    • one year ago
  11. wio Group Title
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    We still double count the ones who break two or more rules, so we have to get rid of them. \(10^{10} \) break both upper and lower case rule \(26^{10} \) break both upper case and digit rule \(26^{10} \) break both lower case and digit rule \(0\) break all three rules, because it must contain at least a digit or letter

    • one year ago
  12. cinar Group Title
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    you'are right, I made a typo..

    • one year ago
  13. wio Group Title
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    So we have \((10+26+26)^{10} - ((10+26)^{10} + (10+26)^{10} + (26+26)^{10} - (10^{10} + 26^{10} + 26^{10})) \)

    • one year ago
  14. wio Group Title
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    Do you understand how I did that?

    • one year ago
  15. cinar Group Title
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    hold on..

    • one year ago
  16. cinar Group Title
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    it is like union of three set..

    • one year ago
  17. wio Group Title
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    Yeah

    • one year ago
  18. wio Group Title
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    Are you doing probability with set theory?

    • one year ago
  19. wio Group Title
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    Discreet math?

    • one year ago
  20. cinar Group Title
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    Discreet math

    • one year ago
  21. wio Group Title
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    So do you or don't you understand how I got what I got?

    • one year ago
  22. cinar Group Title
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    so, AUBUC=A+B+C-AIB-AIC-BIC+AIBIC I=intersection

    • one year ago
  23. wio Group Title
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    Yeah

    • one year ago
  24. cinar Group Title
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    got it..

    • one year ago
  25. cinar Group Title
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    how about part b, any idea..

    • one year ago
  26. wio Group Title
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    Do you have any ideas where to start?

    • one year ago
  27. cinar Group Title
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    let see

    • one year ago
  28. cinar Group Title
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    preceded by a letter means a1 or 1a

    • one year ago
  29. cinar Group Title
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    I am confused..

    • one year ago
  30. wio Group Title
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    I'm pretty sure it means a1

    • one year ago
  31. cinar Group Title
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    hmm, then password cannot be begun by a number..

    • one year ago
  32. wio Group Title
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    Well, one thing to ask is, must all digits be preceded by a number, or just at least one digit?

    • one year ago
  33. cinar Group Title
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    and also no number is successive

    • one year ago
  34. cinar Group Title
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    22 or 555 not allowed

    • one year ago
  35. cinar Group Title
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    a2ddd3y8jj8i898 is ok

    • one year ago
  36. wio Group Title
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    I think a123456789 is also okay, because it has one digit immediately preceded by a letter. They didn't say ALL must follow the rule, just one.

    • one year ago
  37. wio Group Title
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    so 1a23456789 would be ok too.

    • one year ago
  38. cinar Group Title
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    that' why I am confused..

    • one year ago
  39. cinar Group Title
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    listen I need some break to eat something..

    • one year ago
  40. cinar Group Title
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    I am back..

    • one year ago
  41. wio Group Title
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    Ok. So one thing we can take into consideration is that for a password to have a digit and be invalid, it would have to have to be 1... 11.... 111.... basically a bunch of digits in order with no letters in between.

    • one year ago
  42. wio Group Title
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    So one way is 1 digit and then 9 letters, with at least one capital and one lowercase

    • one year ago
  43. wio Group Title
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    So find how many ways we can have a password that is valid in (a) and not valid in (b) and subtract that from (a)

    • one year ago
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