## Search found 2633 matches

- Fri Jun 06, 2008 5:20 am UTC
- Forum: Mathematics
- Topic: A strange distribution
- Replies:
**2** - Views:
**909**

### A strange distribution

This is something I thought of some time ago, but never really found a decent answer to. Suppose you have a set of items, say bingo balls, numbered 1 to n. You draw the items one at a time, and at each draw the items not yet drawn have an equal probability of selection. Before each draw, you make a ...

- Fri Jun 06, 2008 4:05 am UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0432: "Journal 4"
- Replies:
**115** - Views:
**26854**

### Re: "Journal 4" Discussion

Time to throw in another interpretation - when she took his hat, she told him that she was better at classholery than he was. And for a while, he must have thought that he had finally found a worthy adversary. But look how easily she fell for the old "stolen Russian submarine hidden under the f...

- Wed Jun 04, 2008 7:16 am UTC
- Forum: Mathematics
- Topic: poor e
- Replies:
**40** - Views:
**4875**

### Re: poor e

There is one moderately explainable (and somewhat real life-relevant) e - the compound interest problem. For those who haven't come across it, it's something like this: If I put $1 into the bank at 1% p.a., compounded yearly, then this time next year I'll have $1 \times (1 + 1\%)^1 = $1.0100...

- Fri May 30, 2008 7:52 am UTC
- Forum: Mathematics
- Topic: Division by Zero (Please, no new threads about this)
- Replies:
**367** - Views:
**80294**

### Re: Division by Zero (Please, no new threads about this)

2 is typically shorthand for (1+1). 4 us typically shorthand for (1+1+1+1). So for 2+2 != 4, we need (1+1)+(1+1) != (1+1+1+1). This is possible without it being inconsistent -- you just need a very different set of axioms than the usual ones. :) For inconsistencies in general, there are logic syste...

- Wed May 28, 2008 7:11 am UTC
- Forum: Mathematics
- Topic: Monty Revisited
- Replies:
**6** - Views:
**1301**

### Re: Monty Revisited

The line that's always missing is "Monty, who already knows where the prize is, opens (however many doors) that he knows do not contain the prize." Once you've got that there, the conclusion is much more sensible.

- Wed May 28, 2008 7:05 am UTC
- Forum: Mathematics
- Topic: Probability Question - Addition Rule for Multiple Events?
- Replies:
**4** - Views:
**1362**

### Re: Probability Question - Addition Rule for Multiple Events?

The general concept you're trying for, though, is really just a case of combining set theory with induction/iteration. Say you're looking to find P\left(\bigcup_{i=1}^n A_i\right) where A_1, ... A_n are a group of events. Then you can arrange things as follows: \begin{align} P\left(\bigc...

- Mon May 19, 2008 4:11 am UTC
- Forum: Mathematics
- Topic: Advice for math tutoring
- Replies:
**23** - Views:
**2647**

### Re: Advice for math tutoring

Teach understanding, not memorisation (but don't go overboard). If the subject in hand is X, and X is based on the more advanced concept of X', which in turn is based on X'', go a little into X' to show how X actually works, and if questioned on X' explain that X'' exists, but is probably a bit too ...

- Thu May 15, 2008 2:27 am UTC
- Forum: Science
- Topic: Can allergies appear/change?
- Replies:
**18** - Views:
**4215**

### Re: Can allergies appear/change?

And two treatments for allergies are avoidance therapy (where you don't go near the allergen in the hopes that your immune system will "forget" about it being an irritant at some point), and exposure therapy (where you're exposed to very low levels of the allergen in the hopes that your im...

- Thu May 15, 2008 2:04 am UTC
- Forum: Mathematics
- Topic: Can't solve this problem, can someone help?
- Replies:
**15** - Views:
**1515**

### Re: Can't solve this problem, can someone help?

Yakk wrote:[imath]r^2 + r -1 = A(r^2+r)+B[/imath]

Let A = 1/r. Then

[imath]r^2 + r - 1 = r + 1 + B[/imath]

[imath]r^2 -2 = B[/imath]

which is another solution.

Unless you're looking for the A and B that make the equation *always* true. In which case you want values that are independent of r. Think partial fraction decomposition.

- Wed May 14, 2008 7:20 am UTC
- Forum: Mathematics
- Topic: Maths Ver. 2.1.2
- Replies:
**38** - Views:
**5242**

### Re: Maths Ver. 2.1.2

I know the comic's already gone up, but just for the hell of it:

* For improved security, several composite numbers have been defined as "unfactorisable" for use as RSA keys.

* Probability distributions standardised to all return proven random number "4". (http://xkcd.com/221/)

* For improved security, several composite numbers have been defined as "unfactorisable" for use as RSA keys.

* Probability distributions standardised to all return proven random number "4". (http://xkcd.com/221/)

- Wed May 14, 2008 6:54 am UTC
- Forum: Mathematics
- Topic: A random variable question
- Replies:
**10** - Views:
**1720**

### Re: A random variable question

Try calculating the cdf as

[math]F(x) = \int_{-1}^x \frac{3}{8}\left(1-t\right)^2dt[/math]

rather than expanding it out. That seems to give a relatively simple result for me.

[math]F(x) = \int_{-1}^x \frac{3}{8}\left(1-t\right)^2dt[/math]

rather than expanding it out. That seems to give a relatively simple result for me.

- Wed May 14, 2008 4:49 am UTC
- Forum: Mathematics
- Topic: Number sequences
- Replies:
**12** - Views:
**1885**

### Re: Number sequences

There are a couple at this site. That should give you a small start, at least.

- Mon May 12, 2008 1:50 am UTC
- Forum: Mathematics
- Topic: Comparing experimental mean to true mean
- Replies:
**3** - Views:
**1031**

### Re: Comparing experimental mean to true mean

Hmmm ... interesting. Technically, you've got three hypotheses here, rather than the normal two. I suppose you could set it up something like this: \begin{cases}H_0: r = r1 \\ H_0': r = r2\end{cases} (i.e. your 'null hypothesis' is that the rate is equal to r1, and your 'other null hypothesis' -...

- Wed Apr 09, 2008 8:51 am UTC
- Forum: Mathematics
- Topic: Calculus Class T-Shirt
- Replies:
**23** - Views:
**3862**

### Re: Calculus Class T-Shirt

d/dx e

Don't Ever Change.

or

d/dx c = 0

Don't Ever Change.

^{x}= e^{x}Don't Ever Change.

or

d/dx c = 0

Don't Ever Change.

- Mon Apr 07, 2008 7:52 am UTC
- Forum: Science
- Topic: How do you discuss science with a non-scientist?
- Replies:
**61** - Views:
**5409**

### Re: How do you discuss science with a non-scientist?

I'd say there are many more tolerant open minded people who identify as Christians out there than intelligent open minded people who identify as atheists, in terms of percentages of total self identified Christians and atheists. But that has more to do with the fact that calling yourself a Christia...

- Mon Apr 07, 2008 7:35 am UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0407: "Cheap GPS"
- Replies:
**99** - Views:
**20306**

### Re: "Cheap GPS" Discussion

Stickfodder wrote:it's still more effective than my method of finding places i want to go by follow someone who seems to know where they're going

Pfft. That's not your method, that's Dirk Gently's. Still, nice DNA reference.

- Mon Apr 07, 2008 6:42 am UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0210: "90's Flowchart"
- Replies:
**45** - Views:
**21151**

### Re: "90's Flowchart" Discussion

This thread can't die, because nobody explained what "applied Markov chains" are! The Wikipedia page was too symbol-strewn for me to make sense of it. Does the alt-text mean that you can sort-of predict what word a lyric will end with, given the previous verses? Or that you can maybe pred...

- Sun Apr 06, 2008 10:40 am UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0404: "404 - Not Found"
- Replies:
**58** - Views:
**7148**

### Re: comic #404

The alt-text really made this one.

- Wed Apr 02, 2008 4:47 am UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0405: "Journal 3"
- Replies:
**237** - Views:
**36442**

### Re: "Journal 3" discussion

I can see this turning into a fantastic back-and-forth between the two of them, seeking to Mario each other in ever more spectacularly classholish ways. Unfortunately, I can't think of a decent ending for them, as the only options I can think of are (a) mutual destruction, and (b) finally deciding t...

- Wed Apr 02, 2008 4:36 am UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0351: "Trolling"
- Replies:
**179** - Views:
**34297**

### Re: "Trolling Discussion"

Wow, this thread has been dead a while. Anyway, http://www.seeqpod.com (<- legit link) has been rickrolling people on April Fool's day: seeqpod_rickroll_aprilfools.PNG I tried it with other songs, too, and they're doing it for everything. I just thought I'd share that. Not to mention all of the Fea...

- Wed Mar 19, 2008 6:11 am UTC
- Forum: Science
- Topic: Ways to Make a Black hole
- Replies:
**16** - Views:
**1889**

### Re: Ways to Make a Black hole

so that it doesn't get crushed or deformed as you pile more on, Once you reach the stage at which the event horizon forms (actually, I think this happens before that point), wouldn't the pile of styrofoam have to be crushed into a singularity? Not really. Once the event horizon forms (equivalently,...

- Mon Mar 17, 2008 10:44 am UTC
- Forum: Mathematics
- Topic: Please point out where I'm wrong.
- Replies:
**17** - Views:
**2382**

### Re: Please point out where I'm wrong.

Looking back, it was really only SlyReaper's suggestion that I couldn't understand, but I'm not a big fan of inductive proofs in general where they can be avoided. I think I also assumed that you were making the same suggestion as SlyReaper. Yeah that's not surprising. I was a bit tipsy when I sugg...

- Fri Feb 22, 2008 12:13 pm UTC
- Forum: Mathematics
- Topic: 1=0.99999999... as related to fractals
- Replies:
**40** - Views:
**4352**

### Re: 1=0.99999999... as related to fractals

An argument for 1 = 0.9999... that I've always found pretty intuitive is: x = 0.999... therefore 10x = 9.999... therefore 9x = 10x - x = 9 , therefore x = 9x/9 = 1, therefore 0.999... = 1 QED. It seems like it should be possible to extend this style of reasoning to the area of the Sierpenski gasket...

- Fri Feb 22, 2008 11:49 am UTC
- Forum: Mathematics
- Topic: Math Software
- Replies:
**143** - Views:
**148239**

### Re: Can't find good graph drawing software

For Windows, I've always been a fan of GrafEq ( http://www.peda.com ). It's nagware, but the nag screen is fairly innocuous. It's also powerful enough to do some very tricky things - like graphing regions based on inequalities (e.g. x 2 +y 2 < 1), control over colours, cartesian or polar inputs (alt...

- Fri Feb 22, 2008 11:38 am UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0387: "Advanced Technology"
- Replies:
**105** - Views:
**27050**

### Re: "Advanced Technology" Discussion

Even as a single geek, I still think this comic is late - it should have been put out a week and a half earlier so people could have used it on Valentine's Day cards.

Then again, maybe that's why I'm single.

Then again, maybe that's why I'm single.

- Wed Feb 20, 2008 11:08 am UTC
- Forum: Science
- Topic: Only a Theory
- Replies:
**39** - Views:
**5901**

### Re: Only a Theory

I would go a little further than Likpok, and say it's a misunderstanding between theory and Theory. The first, "theory", refers to an idea someone has had but has no proof for, and is often prefixed with "I have a" or "crackpot". The second, "Theory", is a sci...

- Sun Feb 17, 2008 9:42 am UTC
- Forum: Mathematics
- Topic: Philosophical Justification of Indeterminate Forms
- Replies:
**35** - Views:
**3580**

### Re: Philosophical Justification of Indeterminate Forms

When a mathematician who is working explicitly in the real numbers (or integers) talks about infinity, what they're talking about is a process or function that continues without limit. So, if you see an expression such as ∞·0, what they normally mean is something along the lines of lim x -> ∞ (f(x)g...

- Sun Feb 10, 2008 12:57 pm UTC
- Forum: Mathematics
- Topic: Follow-on to the "Why do people hate maths thread"
- Replies:
**21** - Views:
**3212**

### Re: Follow-on to the "Why do people hate maths thread"

The neat thing about the Argand plane is that it's like the Cartesian plane (i.e. your plain old x-y plane) in many respects, but it's got more "information" in it than that. For example, say we have the points z1 = (x1, y1) and z2 = (x2, y2). What is z1 * z2? We don't have any kind of mul...

- Sun Feb 10, 2008 12:00 pm UTC
- Forum: Mathematics
- Topic: Is 0 real?
- Replies:
**43** - Views:
**9620**

### Re: Is 0 real?

Many people have mentioned the identity element of an algebraic structure. Without axiomatically taking such structures to have such an element, we can't do any algebra--i.e. we can't solve equations. For example, these two axioms appear when coming up with many different algebras (groups, rings, f...

- Wed Jan 30, 2008 7:06 am UTC
- Forum: Mathematics
- Topic: Operations On Complex Numbers
- Replies:
**4** - Views:
**1193**

### Re: Operations On Complex Numbers

Did you ever work with surds, like 1 + √5? It's the same idea: Say you have the fraction (1 + 2√3)/(3 + √2), and you want to express it as a number with an integer denominator (because having a √2 on the bottom is really bugging you). Then you take the conjugate of 3 + √2, which is 3 - √2, and the f...

- Wed Jan 30, 2008 6:56 am UTC
- Forum: Mathematics
- Topic: Creative Request- adventures of a Mathematician Superhero?
- Replies:
**34** - Views:
**3822**

### Re: Creative Request- adventures of a Mathematician Superhero?

On the really, really high-end fantasy maths, there's Psychohistory , the statistical science of predicting human behavior. Indon, I was thinking somewhat realistic although fantasy could def apply. He has a villain in real life (his boss) so that is going to be the villain in the comic. Basically ...

- Sun Jan 20, 2008 1:11 pm UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0372: "To Be Wanted"
- Replies:
**143** - Views:
**22792**

### Re: To Be Wanted Discussion

Here's yet another interpretation - Adventure Girl is a metaphorical character, personifying the idea of escape from everyday desk jobs. So at the first level of the comic, we just have the image of AG sailing the seas, preparing to free the Randalls of the world. At the second level, we have one su...

- Wed Jan 02, 2008 7:19 am UTC
- Forum: General
- Topic: INTRO THREAD THE THIRD
- Replies:
**10914** - Views:
**2137248**

### Re: POST HERE FIRST - INTRO THREAD THE THIRD

Hi, I'm ConMan (that's a name, not a title[1]), and I'm from Sydney. My birthdate is one of three powers of two that can be written in d/m/yy format (i.e. 2 digits for the year, and the minimum necessary for date and month). As you might have guessed, I'm a maths (among other things) geek, so I don'...