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BrainDen.com - Brain Teasers

New Logic/Math Puzzles

They can be logical [e.g. honestans/swindlecants or hats on death row], math [e.g. probability, sequences], physics or geometry, especially where intuition might suggest wrong answer.


Important: READ BEFORE POSTING

This forum is for “brain teaser” type logic/math puzzles.

Puzzle: Deductive, analytical, but still requiring some insight - not just homework problems.
They can be "figured out", but it takes some thought.
They can be logical [e.g. honestans/swindlecants or hats on death row], math [e.g. probability, sequences], physics or geometry, especially where intuition might suggest wrong answer.
So there's still an element of surprise, where you might not guess the right result.
Or it might seem impossible until you see it in the right light [hats eg]

If you wish to post a word riddle (for instance, What-Am-I riddle), do it in forum section titled "New Word Riddles".

For clarification on what constitutes a brain teaser, see the following Wikipedia article:
http://en.wikipedia.org/wiki/Brain_teaser

Hint: “Why is the sky blue?” is not a brain teaser. If you’d like to ask a question that doesn’t qualify as a brain teaser, post it in “Others”.

1. Before posting a new riddle, first perform a search to make sure your riddle isn’t one that has previously been posted. For example, if your riddle is, “How many two cent stamps are there in a dozen?”, perform a search of the keyword “stamp” and you will get a list of threads containing the word “stamp”.
If one keyword results in too many hits, search for multiple keywords using the plus sign. Example, try searching for “stamps +dozen” (make sure there is no space between the + sign and the word dozen).
If there is still too much to sift through, you may use Google search incorporated into non-forum pages of this website. For instance, on the BrainDen.com home page, try the search box located in the top right hand corner. Type in “in a dozen” (including the quotes). Note that this Google search is performed only for BrainDen pages (forum and non-forum) and can handle search for words with 3 characters (and less) better than the forum search.

2. When you start a new topic, include a descriptive and unique title. For instance, "What-Am-I - Holiday Theme" or "What-Am-I - Tribute to Descartes" and not just "WAI" or "What Am I".

3. Lately there has been a rash of posts here in "New Puzzles" that are resurrecting old threads. This is fine, if you have something substantial to add or don't agree with the answer. But please don't post to a thread that has been over for a month or longer just to add the same solution that has already been determined. These posts may be deleted without notice.

4. Time limit for editing posts is 10 minutes (except for VIPs). If you think your riddle might need extended editing, try composing it in Notepad first. Then copy/paste into your post. That way you'll still have a few minutes for a final change or two.

5. Basic etiquette - no insulting, disrespectful posts, flame wars, inappropriate words, multiple identities (user names) without admin's approval, do not use copyrighted content (eg. original wording or picture from other website) without appropriate permission etc. Otherwise account might be deleted without notice. Basically - don’t be a jerk.

6. Nit-picking about wording of others' OPs. When solving a riddle, treat the OP as if it has a solution, and then try to find it.
The idea is to find a solution that fits the question without violating any of the conditions. If you would have worded it differently, think it's trivial or it just isn't your cup of tea, let it go and try a different riddle.
Also, please understand that BrainDen is an international community. English is not the primary language of all of our members.
Be considerate of that fact, and if something is not clear, simply ask: "By _____, do you mean _____? or perhaps ____?
We're always happy to clarify, and you'll be doing a service to other solvers as well.

7. Keep your signature short - preferably 1 or 2 lines of simple text. More on signature rules.

8. A few useful tips:
a) you can subscribe to "New Puzzles" and be immediately notified when new puzzle is submitted to the board and thus have a good chance to be the 1st one to solve the puzzle. Go to "New Puzzles" section, click "Forum Options" on the top right hand side and then "Subscribe to this forum". Select your preferred notification method and that's it. Easy.
b) you can track topics - eg. your own puzzles, and be notified whenever someone posts comments on your puzzle. Go to your topic, click "Options" and "Track this topic".
c) use spoilers for answers so that others can enjoy the puzzles as well
d) do not post answers for your own topics in the first post. Wait for some comments. You can give hints and give credits to the first correct solution/member.
e) add RSS feed (from "New Puzzles" section) to your RSS reader (click the orange square which is placed in the bottom left hand side) - to see if new puzzles have been submitted just refresh your feeds (without even opening this site)
f) check 15 latest puzzles - all on 1 page - see New Riddles
g) if you like this site, there is an easy way to spread the word


BrainDen is here for the enjoyment of our members. Moderators will take appropriate action, with or without further warning to ensure a rewarding experience for everyone.
This means that offensive, flaming, disrespectful or harassing content of any type can lead to the termination of an account.


NEW:
Topic starters can mark their threads as solved by simply clicking "Mark Solved" button in the post that includes the right answer 
That pushes the post including correct answer at the top (above the 1st post) and it marks the thread as "Answered" making it easy to open only threads without label "Answered" if you want to be the first one to post the solution.
 
Enjoy the Den 

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