Necro'd because my dad's book, Long for this World came out today and is essentially about the first panel of this strip. It talks about the strip itself, too.

I tried to get my mom to ask Randall to illustrate her upcoming children's biography of Erdös, but she didn't go for it.

## Search found 161 matches

- Tue Jun 22, 2010 9:51 pm UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0568: "Well 2"
- Replies:
**105** - Views:
**25058**

- Mon Mar 01, 2010 6:09 pm UTC
- Forum: Forum Games
- Topic: The Intersecting Geekeries Test
- Replies:
**9** - Views:
**1943**

### Re: The Intersecting Geekeries Test

22/25 http://img7.imageshack.us/img7/4439/terminalvelocity.png Both C and D are correct at terminal velocity. Oy, you're right. And that's a much more blatant mistake than I was expecting, too. :cry: C is the intended answer, as you've probably guessed. I was presumably thinking in definitional...

- Mon Mar 01, 2010 12:33 am UTC
- Forum: Forum Games
- Topic: The Intersecting Geekeries Test
- Replies:
**9** - Views:
**1943**

### The Intersecting Geekeries Test

In my continuing quest to create things that only appeal to the niche-est of niche audiences, I bring you The Intersecting Geekeries Test. Sample question: According to the Borg, what is futile? A. Voltage divided by power. B. Power divided by current squared. C. Voltage times current. D. Current di...

- Thu Feb 18, 2010 11:40 pm UTC
- Forum: Logic Puzzles
- Topic: Train Problem
- Replies:
**16** - Views:
**5126**

- Tue Feb 09, 2010 6:11 pm UTC
- Forum: Logic Puzzles
- Topic: That sequence of operations that always ends with 7
- Replies:
**22** - Views:
**4135**

### Re: That sequence of operations that always ends with 7

I worked this out from scratch this morning, but now that I write it out it looks familiar, so it may not be original. 1. Pick any whole number {0,1,2,3...}. 2. Cube it. 3. Sum the last two digits (if there's only one digit, add 5 to it instead.) 4. Go to step 2. This will always converg...

- Sat Jan 16, 2010 5:49 am UTC
- Forum: Science
- Topic: What does it mean to say that Earth revolves around the sun?
- Replies:
**9** - Views:
**1278**

### What does it mean to say that Earth revolves around the sun?

This is a difficult one to google. I constantly encounter the sentiment that "people used to believe that the sun revolved around the Earth, but now we know it's the other way around." But that can't be strictly correct. All motion is relative. If we hold the sun's position constant, Earth...

- Mon Dec 28, 2009 6:38 am UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0681: "Gravity Wells"
- Replies:
**205** - Views:
**57116**

### Re: "Gravity Wells" Discussion

Should be "still more glorious dawn."

- Wed Oct 21, 2009 1:52 pm UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0652: "More Accurate"
- Replies:
**131** - Views:
**40349**

### Re: "More Accurate" Discussion

Transporter: Tried in Star Trek Insurrection, was too slow and easily countered, so they resorted to Predator drones. The rest seem like super-bombs dressed up with technobabble--a hi-tech planet blows them up before they get close, a low-tech one gets devastated and the Enterprise has to come rescu...

- Thu Aug 06, 2009 1:33 am UTC
- Forum: Logic Puzzles
- Topic: Guess Who?
- Replies:
**22** - Views:
**7531**

### Re: Guess Who?

Good idea. In that case whoever's "winning" wants minimum variance, and the other player wants to maximize variance. As long as both players do a binary search, neither player is winning, and if you change that situation your opponent gets to adjust before you do so it benefits the opponen...

- Thu Aug 06, 2009 12:45 am UTC
- Forum: Logic Puzzles
- Topic: Guess Who?
- Replies:
**22** - Views:
**7531**

### Re: Guess Who?

I think I have a simple, general solution. No matter what strategies are employed, in whatever combination, Player 1's expected number of turns is one fewer than Player 2's. The only thing that can cause Player 2 to win is luck. Therefore, Player 1 wants to decrease the variance as much as p...

- Fri Jul 31, 2009 1:29 am UTC
- Forum: Logic Puzzles
- Topic: Largest Rectangle in Wordspace
- Replies:
**2** - Views:
**1501**

### Re: Largest Rectangle in Wordspace

**Spoiler:**

- Thu Jul 30, 2009 12:07 am UTC
- Forum: Logic Puzzles
- Topic: Decipher the Pioneer Plaque
- Replies:
**17** - Views:
**5291**

### Re: Decipher the Pioneer Plaque

I took a course in college where this was an early assignment. The final was to create a hypothetical alien race that would misinterpret the plaque. The story I wrote for the final is unpublishable because it's crammed full of references to obscure topics covered in the (extremely eclectic) course. ...

- Fri Jun 12, 2009 11:40 pm UTC
- Forum: Logic Puzzles
- Topic: A game.
- Replies:
**2** - Views:
**1044**

### Re: A game.

Hurr. After playing around, it looks like white has a winning strategy in going straight up the middle. When it impacts black's two center pawns, black is forced to move a wing. White then moves back and in the direct of the pawn that just moved. Black has to either move the center pawn to rein...

- Fri May 01, 2009 4:31 am UTC
- Forum: Logic Puzzles
- Topic: Four students, four boxes, one chance at an A grade!
- Replies:
**7** - Views:
**2612**

### Re: Four students, four boxes, one chance at an A grade!

I just proved to myself experimentally that there's no solution. This was clearly a conspiracy to rob me of much needed sleep and trust in humanity.

Edit: Okay, I just saw phlip's hint and I take it back. I'm going to sleep anyway, though.

Edit: Okay, I just saw phlip's hint and I take it back. I'm going to sleep anyway, though.

- Fri May 01, 2009 3:34 am UTC
- Forum: Logic Puzzles
- Topic: Four students, four boxes, one chance at an A grade!
- Replies:
**7** - Views:
**2612**

### Re: Four students, four boxes, one chance at an A grade!

I am completely mystified and suspect there is no solution. I'm going to use exhaustion. Edit: Call the boxes Lucas looks in 1 and 2. Case 1: Matt looks at 3 and 4. Lucas has a 50% chance. Given that Lucas succeeds, Matt has a 2/3rds chance, for 1/3 overall. Case 2: Matt looks at 1 and 2. 25% chance...

- Wed Apr 15, 2009 10:35 pm UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0568: "Well 2"
- Replies:
**105** - Views:
**25058**

### Re: Discussion of "Well 2"

My dad:

I love "The Uncomfortable Truths Well."

Here's one more: "The Uncomfortable Truths Don't Sell Well."

- Sun Mar 01, 2009 6:58 am UTC
- Forum: Logic Puzzles
- Topic: Tough puzzle? Population growth and limit
- Replies:
**2** - Views:
**837**

### Re: Tough puzzle? Population growth and limit

I want it to be that the Earth becomes a black hole, but even if you allow humans to live 12 Km above the surface 11000 years is way too long.

- Fri Feb 27, 2009 8:46 pm UTC
- Forum: Logic Puzzles
- Topic: 169 puzzles (was 'mind trap')
- Replies:
**371** - Views:
**38497**

### Re: 169 puzzles (was 'mind trap')

J Spade's got the Executive one.

- Fri Feb 27, 2009 6:29 am UTC
- Forum: Logic Puzzles
- Topic: 169 puzzles (was 'mind trap')
- Replies:
**371** - Views:
**38497**

### Re: 169 puzzles (was 'mind trap')

Better Know a Country

Legislative Branch: How many United States Senators are there?

Executive Branch: What is the maximum number of continuous years someone may serve as President of the United States?

Judicial Branch: What court is above the United States Supreme Court?

Legislative Branch: How many United States Senators are there?

Executive Branch: What is the maximum number of continuous years someone may serve as President of the United States?

Judicial Branch: What court is above the United States Supreme Court?

- Wed Feb 25, 2009 9:44 am UTC
- Forum: Logic Puzzles
- Topic: Public Crypto without Trapdoor Functions
- Replies:
**38** - Views:
**3075**

### Re: Public Crypto without Trapdoor Functions

I'm asking something more specific than that. If Eve can learn K-2 bits and we're still okay, what's the difference between K = 128 and K = 129? Doesn't the solution reduce to "Alice and Bob transmit as many hashes as they have time to make, then use all the matches to generate a key"?

- Wed Feb 25, 2009 7:37 am UTC
- Forum: Logic Puzzles
- Topic: Super missile, indestructible fort
- Replies:
**21** - Views:
**2797**

### Re: Super missile, indestructible fort

This is an advanced weapon prototype, and always hitting the target means it must have some A.I. in the guidance system. As we know, such a device inevitably gains sentience and turns on its masters. "The intended target"? Intended by whom? The missile is "fired at" the fort by ...

- Wed Feb 25, 2009 5:22 am UTC
- Forum: Logic Puzzles
- Topic: Public Crypto without Trapdoor Functions
- Replies:
**38** - Views:
**3075**

### Re: Public Crypto without Trapdoor Functions

Okay, I see what you're saying. What significance does K have then?

- Tue Feb 24, 2009 10:43 pm UTC
- Forum: Logic Puzzles
- Topic: Public Crypto without Trapdoor Functions
- Replies:
**38** - Views:
**3075**

### Re: Public Crypto without Trapdoor Functions

Right, but she needs the whole key before she can perform decryption. If we're worried about her knowing part of the key then we can simply use the hash of the entire key as the private key. I don't see it. If Eve is allowed to know K/N of the key, then you can just exchange (N-1/N)K bi...

- Mon Feb 23, 2009 7:37 pm UTC
- Forum: Logic Puzzles
- Topic: Iterated Prisoner's Dilemma V2
- Replies:
**30** - Views:
**2789**

### Re: Iterated Prisoner's Dilemma V2

Ouch. I'm guessing my strategy was too nice. Resubmitting one that errs in the other direction.

- Fri Feb 20, 2009 11:17 pm UTC
- Forum: Logic Puzzles
- Topic: Public Crypto without Trapdoor Functions
- Replies:
**38** - Views:
**3075**

### Re: Public Crypto without Trapdoor Functions

Well, they don't have to be independent random numbers--Alice's can be one random number and the 2^K range above it, if you've got a good enough one-way function. Likewise, Bob can choose a number and hash the <i>m</i> numbers above it.

- Fri Feb 20, 2009 5:43 pm UTC
- Forum: Logic Puzzles
- Topic: Public Crypto without Trapdoor Functions
- Replies:
**38** - Views:
**3075**

### Re: Public Crypto without Trapdoor Functions

Proof of concept? Alice generates an ordered list of 2^K random numbers, chooses one of those numbers at random, and hashes it using a function that takes a little more than MC/(2^(K-1)) time, then transmits the random numbers and the one hash. Bob randomly chooses m of the random nu...

- Tue Feb 17, 2009 12:58 am UTC
- Forum: Logic Puzzles
- Topic: Self-reference
- Replies:
**1** - Views:
**1001**

### Re: Self-reference

This statement is true, but people with blue eyes can't assert that it's true without contradicting themselves. Secure a promise to answer two yes-or-no questions as truthfully as possible, and abide by the answers as much as possible. Then ask, "Will your answer to the other question be the sa...

- Fri Feb 13, 2009 2:27 am UTC
- Forum: Logic Puzzles
- Topic: The "Wanion" Hand Cipher
- Replies:
**6** - Views:
**1889**

### The "Wanion" Hand Cipher

I came up with this hand cipher some time in elementary school, and I just remembered it. I'm curious if anyone can come up with a scheme to break it by hand. Enciphering: 1. You and your partner secretly agree on a numbering of the 26 letters of the alphabet, plus the space character. This is your ...

- Mon Jan 26, 2009 11:26 pm UTC
- Forum: Logic Puzzles
- Topic: Sunny w/e
- Replies:
**26** - Views:
**3480**

### Re: Sunny w/e

Objection! (I've been watching Franken v. Coleman for some reason). Isn't it a fallacy to say, under any circumstances, "we can't assign a probability"? Probability is always an expression of lack of information, so lacking more information can't make the assignment impossible,...

- Tue Jan 13, 2009 7:52 pm UTC
- Forum: Logic Puzzles
- Topic: The solution is a two-digit number
- Replies:
**19** - Views:
**3952**

### Re: The solution is a two-digit number

0870678884068983409815824039880670002291 OP: Did you come up with this puzzle on your own? Just curious ... it's quite clever. Yes, I did, thanks! I'm not sure if making the answer a number is the best way to present it, what do you think? It's essentially a red herring. (Or if you're scrolling dow...

- Wed Jan 07, 2009 6:15 pm UTC
- Forum: Logic Puzzles
- Topic: Man at a funeral
- Replies:
**18** - Views:
**4040**

### Re: Man at a funeral

May be a massive hole here I'm missing... He's the step-uncle? I don't see how that works. A is B's step-uncle if 1. A is the sibling, by adoption, of B's parent. In this case, A has siblings (by adoption), so the condition fails. 2. A is the sibling of someone who is B'...

- Wed Jan 07, 2009 6:09 pm UTC
- Forum: Logic Puzzles
- Topic: Choice by coin flipping
- Replies:
**28** - Views:
**5329**

### 3-sided coin *emulation*

You have a normal, fair, 2-sided coin. You need to make a random, unbiased decision among options A, B, and C using only a series of coin flips. Part 1. What method can you use that will minimize the average number of flips necessary? Part 2. Formally prove that no method does better. Edit: Okay, fo...

- Wed Jan 07, 2009 5:59 pm UTC
- Forum: Logic Puzzles
- Topic: Man at a funeral
- Replies:
**18** - Views:
**4040**

### Re: Man at a funeral

Straightforward answer: He is the father of the deceased. Less obvious answer: He is the uncle of the deceased via a now-deceased sibling. Very sketchy answer: No legal relation. The man's father was his clone and thus the two could be said to share a father without being siblings. Arm-amputator...

- Wed Jan 07, 2009 5:38 pm UTC
- Forum: Logic Puzzles
- Topic: The solution is a two-digit number
- Replies:
**19** - Views:
**3952**

### Re: The solution is a two-digit number

Could you explain that a bit more, I still don't fully understand. http://en.wikipedia.org/wiki/International_Standard_Book_Number An ISBN-10 is a 10-digit number that uniquely identifies an edition of a book. It can be recognized if you've worked a lot with books, or by the check property the ...

- Wed Jan 07, 2009 11:32 am UTC
- Forum: Logic Puzzles
- Topic: The solution is a two-digit number
- Replies:
**19** - Views:
**3952**

### Re: The solution is a two-digit number

That is, of course, right. I am pleased and impressed.

- Sun Jan 04, 2009 8:25 pm UTC
- Forum: Logic Puzzles
- Topic: The solution is a two-digit number
- Replies:
**19** - Views:
**3952**

### Re: The solution is a two-digit number

Re the first: It's not quite that obnoxious. I have read the forum rules.

Re the second: No. Although if your plan is to post 90 guesses one at a time, I can confirm that will, in a sense, work. Maybe I should've given a larger solution space.

Re the second: No. Although if your plan is to post 90 guesses one at a time, I can confirm that will, in a sense, work. Maybe I should've given a larger solution space.

- Sun Jan 04, 2009 10:08 am UTC
- Forum: Logic Puzzles
- Topic: A Code
- Replies:
**2** - Views:
**972**

### Re: A Code

Thanks for the puzzle.

Your fourth character, 268, should be 201.

Your fourth character, 268, should be 201.

- Sun Jan 04, 2009 9:21 am UTC
- Forum: Logic Puzzles
- Topic: The solution is a two-digit number
- Replies:
**19** - Views:
**3952**

### Re: The solution is a two-digit number

No, not the answer. When you get it you'll know you've gotten it.

- Sat Jan 03, 2009 10:25 pm UTC
- Forum: Logic Puzzles
- Topic: The solution is a two-digit number
- Replies:
**19** - Views:
**3952**

### Re: The solution is a two-digit number

I may have to post hints for this; it's pretty obnoxious. But I'll give it a week or so.

- Sat Jan 03, 2009 9:12 pm UTC
- Forum: Logic Puzzles
- Topic: The solution is a two-digit number
- Replies:
**19** - Views:
**3952**

### The solution is a two-digit number

0870678884068983409815824039880670002291