BrainDen.com - Brain Teasers

# EventHorizon

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1. ## Boxes and Rat

(by me ) (fyi, the answer to 4 ended up pretty interesting)
2. ## Shuffling a lot of cards

I'll venture an initial guess for a good number of rounds to be twice the number of players, and I base this guess on absolutely nothing. Though players+1 seems like a good guess too. Just curious, when would you call the decks randomized? It seems you could get to the state where every situation could occur, but they wouldn't all have the same probability of occurring (and it may be impossible to reach uniformly random regardless of the number of rounds). That said, I'm thinking something like either 1/e or 1-(1/e) will be the optimal proportion of cards to pass (or maybe something
3. Edit reason: Bug in resume code
4. Well, if any two of {A,B,C} have the same prime factor, then the other must (trivial to prove). So we are looking for a case where all 3 are relatively prime. I'm thinking my approach will involve lots of modular arithmetic, but nothing of note to report right now. And given there's a prize on this one, I'm thinking it's been tried before by people more familiar with the necessary maths to solve it (I know next to nothing about rings/fields/etc). Still interesting though, so I'll play with it for a while.
5. I could have been more rigorous in a number of spots, but I think the main idea is sound. Thoughts?
6. You misunderstood the method of choosing the elements of the column marked '0' It is not simply the fibonacci numbers plus one. For instance, the row starting with 4 would require you to find the 4 in the columns with positive integers. It occurs in the column marked '1' and in the row beginning with 1. To the right of that is a 7, so adding 1 to that makes it an 8, not 9 (the fibonacci+1). The next number on that row happens to be the 12 that wouldn't occur anywhere if choosing fib+1.
7. Yup, that's the easy way I hinted at.
8. Nana7 and rasar619 have the question right (a trillion is an insignificant fraction compared to the potential gold from the box), but both are low on the maximum payout. And as for the time limit, 24 hours was much more than is needed...even to max out the box. Here are two new questions... 1. What is the maximum amount of gold you could get out of the box? (in the form "5*(2^X)" dollars worth) 2. What is the shortest amount of time allowed to repay the debt that is still manageable? (Assume 1 second per button press, 3 seconds per button hold, and ignore any travel time) (FY
9. You are approached by a man holding a strange looking box. The box has 6 chambers numbered 1 through 6. Each chamber contains 1 token. Each chamber also has two buttons on it with labels A and B. Button A will remove a token from the chamber and add two tokens to the next higher numbered chamber (if it exists). Button B will remove a token from the chamber and swap the contents of the next two higher numbered chambers (if they exist). Chamber 6 has an extra button, C, which will remove a token from chamber 6 and cause the box to magically produce a dollar's worth of gold. If h
10. It's not ebay, simply because eBay exists and the person who made this contest wouldn't name his new company eBay. From the contest page, someone has won the \$10,000. Once they release more information, I'll update the thread. I'd like a copy of the key so I can try and solve the puzzle myself. Also, where the key was found would be interesting.
11. Source page with contest info Solve this system of equations and find the "key" to discover the new company name. Be the first to find it and you win \$10,000. Also, to get the \$10,000 you need to sign a nondisclosure agreement. So if you do find the answer... I guess you shouldn't post it.
12. Hey Braindenizens. The posts on seem to have stopped, so I thought I would simplify it a little to try and find an eventual solution. 1. Given a well shuffled deck of 8 cards (numbered 1 through 8), what is the probability that when the cards are dealt out that no card's number will reflect the order it was dealt? (i.e., card labelled 1 is not dealt first, card labelled 2 is not dealt second, etc) 2. What is the probability in terms of N, where N is now the number of cards in the deck? 3. What is the probability if we use an infinite deck of cards? (yes, take the limit as N app
13. Agreed, it's all downhill after you get a theme song.
14. EventHorizon, started well, but perhaps swayed somewhere in between. See the Spoiler.
15. A funny application of this new found phenomena: When people pull the waist-line of their pants out to show how much weight they've lost, you can show them the math and convince them they didn't really lose much circumference. edit: Just don't start with, "assume the radius of your waist is that of the earth..." as it might make them feel bad.
16. Also, it's interesting there are 4 responses and 4 different answers
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