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lopus
 2 years ago
Best ResponseYou've already chosen the best response.0http://www.khanacademy.org/math/probability/v/probabilityusingcombinations

wio
 2 years ago
Best ResponseYou've already chosen the best response.1a) 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.

wio
 2 years ago
Best ResponseYou've already chosen the best response.1Now 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?

cinar
 2 years ago
Best ResponseYou've already chosen the best response.0listen I'll be right back ok, give me couple minutes, I need to do something..

wio
 2 years ago
Best ResponseYou've already chosen the best response.1\( (26 +26)^{10}\) Have no digit \( (26+10)^{10} \) Have no lower case \((26+10)^{10} \) Have no upper case

wio
 2 years ago
Best ResponseYou've already chosen the best response.1We 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

cinar
 2 years ago
Best ResponseYou've already chosen the best response.0you'are right, I made a typo..

wio
 2 years ago
Best ResponseYou've already chosen the best response.1So we have \((10+26+26)^{10}  ((10+26)^{10} + (10+26)^{10} + (26+26)^{10}  (10^{10} + 26^{10} + 26^{10})) \)

wio
 2 years ago
Best ResponseYou've already chosen the best response.1Do you understand how I did that?

cinar
 2 years ago
Best ResponseYou've already chosen the best response.0it is like union of three set..

wio
 2 years ago
Best ResponseYou've already chosen the best response.1Are you doing probability with set theory?

wio
 2 years ago
Best ResponseYou've already chosen the best response.1So do you or don't you understand how I got what I got?

cinar
 2 years ago
Best ResponseYou've already chosen the best response.0so, AUBUC=A+B+CAIBAICBIC+AIBIC I=intersection

cinar
 2 years ago
Best ResponseYou've already chosen the best response.0how about part b, any idea..

wio
 2 years ago
Best ResponseYou've already chosen the best response.1Do you have any ideas where to start?

cinar
 2 years ago
Best ResponseYou've already chosen the best response.0preceded by a letter means a1 or 1a

wio
 2 years ago
Best ResponseYou've already chosen the best response.1I'm pretty sure it means a1

cinar
 2 years ago
Best ResponseYou've already chosen the best response.0hmm, then password cannot be begun by a number..

wio
 2 years ago
Best ResponseYou've already chosen the best response.1Well, one thing to ask is, must all digits be preceded by a number, or just at least one digit?

cinar
 2 years ago
Best ResponseYou've already chosen the best response.0and also no number is successive

wio
 2 years ago
Best ResponseYou've already chosen the best response.1I 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.

wio
 2 years ago
Best ResponseYou've already chosen the best response.1so 1a23456789 would be ok too.

cinar
 2 years ago
Best ResponseYou've already chosen the best response.0that' why I am confused..

cinar
 2 years ago
Best ResponseYou've already chosen the best response.0listen I need some break to eat something..

wio
 2 years ago
Best ResponseYou've already chosen the best response.1Ok. 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.

wio
 2 years ago
Best ResponseYou've already chosen the best response.1So one way is 1 digit and then 9 letters, with at least one capital and one lowercase

wio
 2 years ago
Best ResponseYou've already chosen the best response.1So find how many ways we can have a password that is valid in (a) and not valid in (b) and subtract that from (a)
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