Stat Problem
- From: edricflo@xxxxxxxxx
- Date: Mon, 7 Jul 2008 16:40:58 -0700 (PDT)
A computer hacker is trying to break into a computer system by
guessing the system administrator's password. The hacker can try 9
passwords a minute, but if he tries unsuccessfully for more than 10
minutes a day, he will get caught. If he limits his attempts to less
time each day, he will not get caught. The hacker knows that the
administrator's password is at least 6 and at most 12 characters long,
does not contain any character that is not a number, an uppercase
letter, or a lowercase letter (no special characters such as spaces,
punctuation marks, dollar signs, etc.), and that the first character
is a letter. Case matters, and characters can be repeated.
How many passwords are there that start with a letter, contain only
numbers and upper and lowercase letters, and are at least 6 and at
most 12 characters long?
What fraction of the passwords that start with a letter, contain only
numbers and upper and lowercase letters, and are at least 6 and at
most 12 characters long can the hacker try in 10 years without getting
caught? (assume that every year lasts 365.25 days)
.
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