## Search found 206 matches

- Fri Jul 26, 2013 1:46 am UTC
- Forum: Mathematics
- Topic: How Can Humans Be More Random?
- Replies:
**12** - Views:
**4151**

### Re: How Can Humans Be More Random?

@skeptical scientist: I somehow missed that link earlier (even though it was the entire first line of your post, oops). That's exactly the sort of thing I'm looking for! Awesome.

- Thu Jul 25, 2013 3:07 pm UTC
- Forum: Mathematics
- Topic: How Can Humans Be More Random?
- Replies:
**12** - Views:
**4151**

### Re: How Can Humans Be More Random?

I like the second hand and letters suggestions. And also the discussion about normal numbers. I'll admit I was sort of looking for a method that works no matter where I'm walking and what I'm carrying. For example, here's one I already have. It generates a random sequence of yes/no decisions, using ...

- Thu Jul 25, 2013 12:20 am UTC
- Forum: Mathematics
- Topic: Show us your articles! Or what's your Erdos number?
- Replies:
**187** - Views:
**272962**

### Re: Show us your articles! Or what's your Erdos number?

2 (through Ronald Graham). Yesssssss

Here's the paper! We prove that the internet exists, unless a wire costs an integer number of dollars.

Here's the paper! We prove that the internet exists, unless a wire costs an integer number of dollars.

- Wed Jul 24, 2013 11:18 pm UTC
- Forum: Mathematics
- Topic: How Can Humans Be More Random?
- Replies:
**12** - Views:
**4151**

### How Can Humans Be More Random?

Sometimes I'm walking around without a coin, deck of cards, etc..., and I want to make a random decision. Of course humans are terrible at being truly random , so we need a system to avoid being biased. Do you know a good PRAG (pseudo-random anything generator) that people can use to generate some r...

- Tue Jul 23, 2013 3:46 am UTC
- Forum: Individual XKCD Comic Threads
- Topic: 1214: "Geoguessr"
- Replies:
**102** - Views:
**33037**

### Re: 1214: "Geoguessr"

I got a haunted town in Russia: Challenge Link (skip to the fourth location and ignore the horrible guesses)

There are at least two ghosts there.

There are at least two ghosts there.

- Thu Jul 18, 2013 11:32 pm UTC
- Forum: Mathematics
- Topic: Tips for practicing for the AMC
- Replies:
**2** - Views:
**1349**

### Re: Tips for practicing for the AMC

Speaking as someone who's teaching at a math camp right now, where most of the campers are middle or high schoolers who want to get into Olympiad math... I can't say "Read this book and this book to do well on the AMC." It doesn't work like that, (un)fortunately. Here's what I can say: ...

- Sun Jul 14, 2013 3:13 am UTC
- Forum: News & Articles
- Topic: Take A Louisiana Literacy Test!
- Replies:
**87** - Views:
**21307**

### Re: Take A Louisiana Literacy Test!

The equivalent for math: Jewish Problems . Used in anti-Semitic Russia to prevent Jews from attending a university. The admissions department would fire these problems at a prospective student one by one, until they failed to answer. I was told that these problems were carefully designed to have ele...

- Sat Jul 13, 2013 2:01 am UTC
- Forum: Mathematics
- Topic: Random problems with diagrams
- Replies:
**6** - Views:
**1774**

### Re: Random problems with diagrams

Wow, these are hard. And I'm saying this as someone who's done a lot of Olympiad geometry. Comment: the third problem falls to coordinates pretty easily. I haven't solved the other two yet, and I don't want to bash those. There's definitely a silly length-computing solution to problem 2 (i.e. we can...

- Thu Jul 04, 2013 3:46 pm UTC
- Forum: Mathematics
- Topic: Clever High School Math Problems
- Replies:
**31** - Views:
**13806**

### Re: Clever High School Math Problems

Nothing works for bases 16 through 36. Unfortunately, 38 looks like it would take way too long to run.

I doubt it's ever possible above 14, but I don't see any way to prove it either. The conditions are all too global.

I doubt it's ever possible above 14, but I don't see any way to prove it either. The conditions are all too global.

- Tue Jul 02, 2013 12:54 am UTC
- Forum: General
- Topic: Hype your ripe snipes 'n' gripes
- Replies:
**28619** - Views:
**3486808**

### Re: Pant Thread (because we need more panting)

Adacore wrote:I think rand(0,99)*10 + rand(0,10), unless this was a joke I missed.

And remember, if you think you can pick a "uniformly random integer between -∞ and ∞", then you need to call rand(all).

- Tue Jun 25, 2013 12:17 am UTC
- Forum: Mathematics
- Topic: Could Rev. Bayes evaluate a suspect horse tipster?
- Replies:
**3** - Views:
**1084**

### Re: Could Rev. Bayes evaluate a suspect horse tipster?

That is a classic scam, but I think 100 predictions is too many to make it work. It is possible that the guesser somehow cheated on the first 100 predictions (e.g. published them after the races ended). In real life, that's what I would suspect. Oh, yeah, if this is an actual real life scenario, don...

- Mon Jun 24, 2013 6:56 pm UTC
- Forum: Mathematics
- Topic: Could Rev. Bayes evaluate a suspect horse tipster?
- Replies:
**3** - Views:
**1084**

### Re: Could Rev. Bayes evaluate a suspect horse tipster?

So, he's predicted 160 races and had 31 winners. Thus, we can estimate he has a ~19% chance of being correct on any given race. Well, maybe the guesser actually got worse over time for some reason. However, unless you already have a reason to suspect this, it doesn't seem probable: both getting 25 o...

- Mon Jun 10, 2013 10:15 pm UTC
- Forum: Computer Science
- Topic: Non-Erasable Turing Machine
- Replies:
**1** - Views:
**2835**

### Non-Erasable Turing Machine

Let's say you have a Turing Machine without an eraser. That is, cells on its tape can be either blank or shaded. The machine can shade in a cell, but can never erase a shaded cell. Is this machine still Turing complete? If not, what can it compute? I don't see any obvious way to use this machine to ...

- Fri Jun 07, 2013 6:56 pm UTC
- Forum: Logic Puzzles
- Topic: How not to write a CSPRNG
- Replies:
**4** - Views:
**4669**

### Re: How not to write a CSPRNG

Here's my stab at this. 195, 38, 216, 186, 68. I'm pretty sure these are right, with the exception that they might be off by 2. I don't know the generator, but it's pretty clear it's generating 8-bit numbers. If you take each number in the sequence and look at only the bit with value...

- Wed Jun 05, 2013 11:15 pm UTC
- Forum: Logic Puzzles
- Topic: Hat puzzle - 6 (or n) randomly coloured hats in a circle.
- Replies:
**14** - Views:
**9407**

### Re: Hat puzzle - 6 (or n) randomly coloured hats in a circle

Cool variation, snowyowl. No matter what strategy the prisoners use, all 6 of them guess correctly exactly 1/6 of the time. Therefore, in a hypothetical winning strategy, every hat configuration must lead to exactly one of the prisoners guessing correctly. Now, in this hypothetical winning strategy,...

- Fri May 31, 2013 2:16 pm UTC
- Forum: Individual XKCD Comic Threads
- Topic: 1219: "Reports"
- Replies:
**30** - Views:
**7158**

### Re: 1219: "Reports"

Re the alt text, I laugh at posters which try to abuse the bigger-numbers-are-more-exciting gimmick. "Rising gas prices rob us of more than ten milllion dollars every day!" (Well, considering there are more than 300 million people just in the US, that's about 4 cents each.) "If everyo...

- Sun May 26, 2013 4:31 pm UTC
- Forum: Logic Puzzles
- Topic: My Hobby: Steganography
- Replies:
**54** - Views:
**20752**

### Re: My Hobby: Steganography

Nice. Snowyowl, for some reason, your image is greatly visually pleasing.

Figured out one part of it:

Figured out one part of it:

**Spoiler:**

- Thu May 23, 2013 9:18 pm UTC
- Forum: Mathematics
- Topic: Nice proof of Euclid's Lemma?
- Replies:
**26** - Views:
**10412**

### Re: Nice proof of Euclid's Lemma?

You could start by trying to prove that any multiple of 2 always needs 2 in any factorisation - but then I guess you're better off just proving that the integers are a principle ideal domain. It's not hard for 2, or any specific number. Here: by inspection, Z/2Z is an integral domain, hence 2 is pr...

- Wed May 22, 2013 9:40 pm UTC
- Forum: Logic Puzzles
- Topic: Alien abduction
- Replies:
**33** - Views:
**15775**

### Re: Alien abduction

Can they open a door without touching the doorknob? If the puzzle has general no-cheating rules, the only obvious thing they can choose is how long to wait between each door. They just have to hope the other person chooses a time close to theirs. So, the task is like a round from the not-very-fun Ps...

- Wed May 22, 2013 3:47 pm UTC
- Forum: Forum Games
- Topic: Integer Wars - Round 3
- Replies:
**61** - Views:
**6919**

### Re: Integer Wars - Round 2

/in

7 (15 points, minus [next poster's/2])

7 (15 points, minus [next poster's/2])

- Wed May 22, 2013 1:06 pm UTC
- Forum: Mathematics
- Topic: Minimizing surface area of an arbitrary quadrilateral prism
- Replies:
**4** - Views:
**3293**

### Re: Minimizing surface area of an arbitrary quadrilateral pr

Even if it's not what they meant, the general problem " Given side lengths s1, s2, s3, ..., sN, characterize the maximum-area polygon that uses those side lengths in order " is interesting. Also, it has a very elegant and surprising solution. It's one of the only geometry problems that I l...

- Sun May 19, 2013 9:03 pm UTC
- Forum: Mathematics
- Topic: Help needed for a mathematical proof
- Replies:
**3** - Views:
**2416**

### Re: Help needed for a mathematical proof

Currently, where you are in your inductive proof, you've effectively split the sum you want into two sums. Look at the second sum - it's the same as the one in your inductive hypothesis, just with an extra term for c=k-2, right? You can handle that. The first sum is a little trickier, but it falls t...

- Sun May 19, 2013 7:38 pm UTC
- Forum: General
- Topic: ITT: we make what-if Slightly Worse
- Replies:
**13** - Views:
**10142**

### Re: ITT: we make what-if Slightly Worse

Under the standard threads-not-in-Forum-Games rules, I believe I get to pose a question now.

I like dudiobugtron's idea of slightly changing current what-ifs. So, here's my question:

What if everyone who took the SAT guessed on every multiple-choice question? Who would benefit the most?

I like dudiobugtron's idea of slightly changing current what-ifs. So, here's my question:

What if everyone who took the SAT guessed on every multiple-choice question? Who would benefit the most?

- Fri May 17, 2013 5:21 pm UTC
- Forum: General
- Topic: ITT: we make what-if Slightly Worse
- Replies:
**13** - Views:
**10142**

### Re: ITT: we make what-if Slightly Worse

Is this the most expensive* music video ever? *in terms of wool used. Good question, dudiobugtron! To start off, we'll have to determine exactly how much wool the Walkie Talkie Man video uses. The correct unit for wool is the little-known "sheepshead", defined as the amount of wool a farm...

- Fri May 17, 2013 3:32 pm UTC
- Forum: Individual XKCD Comic Threads
- Topic: 1213: "Combination Vision Test"
- Replies:
**159** - Views:
**64715**

### Re: 1213: "Combination Vision"

I saw the 42 just looking at the image (well, I thought it said 92), but I don't have synesthesia. I mean, if you told me a number or a weekday, I could associate it with a color. But if you asked me again later, Wednesday might change from blue to dark green. I agree with the previous posters, I wo...

- Fri May 10, 2013 12:54 pm UTC
- Forum: Logic Puzzles
- Topic: "Projectors" and other Math Puzzles by Vlad Mitlin
- Replies:
**14** - Views:
**6769**

### Re: "Projectors" and other Math Puzzles by Vlad Mitlin

Oh, dang, you're right. I only thought about 1000 and 1978 when I was testing the claim.

Can I get out of this by saying that m is not zero for the two numbers 1978 and 1000 we're interested in?

Can I get out of this by saying that m is not zero for the two numbers 1978 and 1000 we're interested in?

- Fri May 10, 2013 12:50 pm UTC
- Forum: Individual XKCD Comic Threads
- Topic: 1210: "I'm so random"
- Replies:
**242** - Views:
**39561**

### Re: 1210: "I'm so random"

My friends and I agreed a few years ago that the correct response to "Name a random word" is "vineyard".

If you want the second-most-random word, take "hootenanny". Going down the list, there is then "marble", "pizzerias", and "squelch".

If you want the second-most-random word, take "hootenanny". Going down the list, there is then "marble", "pizzerias", and "squelch".

- Thu May 09, 2013 4:01 pm UTC
- Forum: Logic Puzzles
- Topic: "Projectors" and other Math Puzzles by Vlad Mitlin
- Replies:
**14** - Views:
**6769**

### Re: "Projectors" and other Math Puzzles by Vlad Mitlin

Divisor Let threes(n) be the number of threes dividing into n. For example threes (2)=0, threes (18)=2, threes (729)=6. Claim: threes (n k -1)= threes (n-1)+ threes (k). Proof: Let m= threes (n-1), and write n=d3 m +1, where d isn'...

- Thu May 02, 2013 1:01 am UTC
- Forum: General
- Topic: The Worst Superpower
- Replies:
**142** - Views:
**33233**

### Re: The Worst Superpower

Isn't there some guy who'll pay a million dollars to anyone who proves they have magic powers? If so, most of the powers in this thread have at least one use. Terror Island gives us an interesting superpower: the power that everyone knows you are a dentist. Even if you're not actually a dentist, eve...

- Wed Apr 10, 2013 8:16 pm UTC
- Forum: Logic Puzzles
- Topic: A variation of the "Impossible puzzle"
- Replies:
**10** - Views:
**5880**

### Re: A variation of the "Impossible puzzle"

I think I have an answer. The numbers are 5 and 6. S has 11, which isn't decomposable into the sum of two primes, so he says "You can't know the sum". P has 30, so to her, S could have 11 (5+6) or 17 (2+15). So she says "I still don't know your sum." S...

- Tue Apr 02, 2013 7:09 pm UTC
- Forum: Computer Science
- Topic: Pumping Lemma and Regular languages - Is this proof correct?
- Replies:
**10** - Views:
**7785**

### Re: Pumping Lemma and Regular languages - Is this proof corr

There are indirect-but-easier proofs, too. For example,

**Spoiler:**

- Fri Mar 22, 2013 9:59 pm UTC
- Forum: Mathematics
- Topic: (Semi homework) Recursive polynomial functions
- Replies:
**5** - Views:
**2090**

### Re: (Semi homework) Recursive polynomial functions

It's still false, even under that convention, if p(x)=0, f(x)=17. But hey, it's true when n>0, and the zero polynomial is weird anyway. One approach is induction. Say p(x) = a 0 +a 1 x+a 2 x 2 +...+a n x n . Then you already know (from your inductive hypothesis) that the a 0 +a 1 x+a 2 x 2 +...+a n-...

- Tue Mar 12, 2013 1:37 pm UTC
- Forum: Logic Puzzles
- Topic: Mother of All Puzzles
- Replies:
**129** - Views:
**91662**

### Re: Mother of All Puzzles

Can you spot any differences? No, and I assumed that was the point, but everything I've tried so far has failed: nodifference.htm nodifferences.htm same.htm double.htm none.htm identical.htm Do I just need to find the right synonym? Or am I heading in the wrong direction? Regarding level 5: Yea...

- Tue Mar 12, 2013 2:22 am UTC
- Forum: Mathematics
- Topic: Direction to study for Lambert W function?
- Replies:
**8** - Views:
**3854**

### Re: Direction to study for Lambert W function?

The Lambert W function was invented because people like you wanted to solve annoying equations like 2^x = x^2. That's essentially it's sole use. That's also the motivation for its definition as the inverse of xe x . ("Hey, I wanna solve the equation xe x =5, but I can't do it... I know, I'll ju...

- Fri Mar 01, 2013 4:53 pm UTC
- Forum: Mathematics
- Topic: Discontinituous increasing function?
- Replies:
**20** - Views:
**3845**

### Re: Discontinituous increasing function?

Even better, and surprisingly, an increasing function is differentiable almost everywhere.

- Fri Feb 22, 2013 8:39 pm UTC
- Forum: Mathematics
- Topic: Integer Factorization of large semiprimes
- Replies:
**6** - Views:
**4729**

### Re: Integer Factorization of large semiprimes

So. This is a nice O(n 1/4 ) algorithm, and the method you use to get the congruence is pretty slick. However, the algebra crunching around your algorithm hides a much simpler description. It goes like this (I'll use one of your examples): Say we're factorizing 8791, and we get to attempt 3. So 3*87...

- Sun Feb 03, 2013 4:10 pm UTC
- Forum: Logic Puzzles
- Topic: Flow
- Replies:
**17** - Views:
**12457**

### Re: Flow

Right, that's why Step 2 breaks down for some Flow puzzles.

- Thu Jan 31, 2013 11:31 pm UTC
- Forum: Forum Games
- Topic: Inverse "I would rather"
- Replies:
**131** - Views:
**16764**

### Re: Inverse "I would rather"

I would rather get a book published than live in a mansion in any country on Earth I wanted.

- Tue Jan 29, 2013 11:34 pm UTC
- Forum: Logic Puzzles
- Topic: Flow
- Replies:
**17** - Views:
**12457**

### Re: Flow

No problem. Here we go: It's been established that uniqueness doesn't hold for every Flow puzzle, so to show off corners deductions, I'll use a Numberlink instead. Here's the first few steps I took in solving this puzzle, which is quite susceptible to corners logic. numberlink.PNG 1:...

- Sat Jan 26, 2013 3:50 pm UTC
- Forum: Logic Puzzles
- Topic: One line indecipherable cipher
- Replies:
**6** - Views:
**3790**

### Re: One line indecipherable cipher

It almost looks like a mathematical formula, where if you figure out the values of "SUR", "PBH", and "HPN", you can figure out a final number for the answer.

Do any of the other clues have three-letter acronyms, or for that matter, any other similarities to this one?

Do any of the other clues have three-letter acronyms, or for that matter, any other similarities to this one?