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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

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December 14th, 2006, 07:07 AM   #1
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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. )
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December 14th, 2006, 11:46 AM   #2
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From: I'm a figment of my own imagination :?

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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.
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December 14th, 2006, 11:59 AM   #3
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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!)
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December 15th, 2006, 06:29 PM   #4
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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.
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December 16th, 2006, 03:48 AM   #5
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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.
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December 16th, 2006, 04:29 PM   #6
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Obviously, Einar has not taken my hint. Is he even still using My Math Forum?
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December 17th, 2006, 05:21 AM   #7
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Not sure. His post number has been constant at 15 for a while, as I remember.
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December 19th, 2006, 03:22 PM   #8
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It's a lot easier to just move a topic than to leave a note for the moderator and hope he finds it!
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December 20th, 2006, 04:44 AM   #9
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Thanks!
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