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 View Poll Results: Read the question below, and then answer this poll: A. 100% 0 0% B. 22.5% 0 0% C. 38.97% 0 0% D. 45% 5 100.00% E. 0% 0 0% F. 11.25% 0 0% G. 90% 0 0% Voters: 5. You may not vote on this poll

 December 14th, 2006, 07:07 AM #1 Senior Member   Joined: Dec 2006 Posts: 1,111 Thanks: 0 Crack the lock! Suppose that I'm trying to break a typical 3-roller bicycle lock with each roller having the numbers 0-9 on it, making 1000 possible combinations. Further suppose that I am trying to break the lock by a brute force decryption attack, such that I start with combination 000 and work to combination 999. Also, suppose that I can try out 1 combination every 3 seconds, such that it would take me 50 minutes to check all probabilities. What is the probability that I will crack the lock in only 22.5 minutes? ( I'll post the answer in a few days, even though I imagine a lot of you will be able to figure out what it is pretty quickly. )
 December 14th, 2006, 11:46 AM #2 Senior Member   Joined: Nov 2006 From: I'm a figment of my own imagination :? Posts: 848 Thanks: 0 It seems obvious from the poll that people are having no trouble figuring this one out. It's hardly a college level question. I'm in high school, have taken a single half-credit course in prob/stats and know the answer.
 December 14th, 2006, 11:59 AM #3 Senior Member   Joined: Dec 2006 Posts: 1,111 Thanks: 0 True, and it occurred to me later that I should have posted it in the high school forum. I think I'll move it there. (If I can figure out how!)
 December 15th, 2006, 06:29 PM #4 Senior Member   Joined: Nov 2006 From: I'm a figment of my own imagination :? Posts: 848 Thanks: 0 I don't think that you can move it to the high school section, but you can request that the moderator, i.e., Einar, move it there. Einar: to move a post, once you have it opened, click on the move post icon at the bottom of the screen.
 December 16th, 2006, 03:48 AM #5 Senior Member   Joined: Dec 2006 Posts: 1,111 Thanks: 0 The answer to this question, as everyone (who voted) seemed to be able to figure out quite easily, was choice D, or 45 %. Since the lock could be positively broken (100% chance) in 50 minutes, then after 22.5 minutes (45% of 50 minutes), 45% of the possible combinations would have been run through, and naturally there would be a 45% chance of breaking the lock.
 December 16th, 2006, 04:29 PM #6 Senior Member   Joined: Nov 2006 From: I'm a figment of my own imagination :? Posts: 848 Thanks: 0 Obviously, Einar has not taken my hint. Is he even still using My Math Forum?
 December 17th, 2006, 05:21 AM #7 Senior Member   Joined: Dec 2006 Posts: 1,111 Thanks: 0 Not sure. His post number has been constant at 15 for a while, as I remember.
 December 19th, 2006, 03:22 PM #8 Senior Member   Joined: Nov 2006 From: I'm a figment of my own imagination :? Posts: 848 Thanks: 0 It's a lot easier to just move a topic than to leave a note for the moderator and hope he finds it!
 December 20th, 2006, 04:44 AM #9 Senior Member   Joined: Dec 2006 Posts: 1,111 Thanks: 0 Thanks!

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