851 replies to this topic

[chgocubs99]

So while I was sitting in the airport for 9 hours yesterday, I bought this book. It's in the other room and I don't remember the title. Anyway, the point is that they talk about factorials in the book and how the whole computer world is based off of them and if they were ever a way to figure out how to factor extremely large numbers quickly, the whole think would send us back to a non-electronic era since nothing would be secure.So is that stuff accurate?

[BigDMcGee]

what's your favorite number sequence in Pi, and what digit does it first appear at?

[pckt10s]

is long division overrated?

[Dirtydutch]

A little word problem, to test Yorke's practical skills:If Dutch were to have unprotected sex with:1 girl with a .04% chance of being HIV-positive, one with a .002% chance, and a third with a 2% chance, statistically speaking, how likely would it be that I made it up?

[ShakeZuma]

Dirtydutch, on Tuesday, April 15th, 2008, 4:15 AM, said:

A little word problem, to test Yorke's practical skills:If Dutch were to have unprotected sex with:1 girl with a .04% chance of being HIV-positive, one with a .002% chance, and a third with a 2% chance, statistically speaking, how likely would it be that I made it up?

atlanta, right? 2%.YORKE: 2 + 2 = _______

[hblask]

chgocubs99, on Tuesday, April 15th, 2008, 1:40 AM, said:

So while I was sitting in the airport for 9 hours yesterday, I bought this book. It's in the other room and I don't remember the title. Anyway, the point is that they talk about factorials prime number factorization in the book and how the whole computer world is based off of them and if they were ever a way to figure out how to factor extremely large numbers quickly, the whole think would send us back to a non-electronic era since nothing would be secure.So is that stuff accurate?

FYP, I think. I haven't heard of factorials being involved in cryptography, it's all about really big prime numbers.I'll let LLY address the rest of it....

[LongLiveYorke]

chgocubs99, on Tuesday, April 15th, 2008, 2:40 AM, said:

So while I was sitting in the airport for 9 hours yesterday, I bought this book. It's in the other room and I don't remember the title. Anyway, the point is that they talk about factorials in the book and how the whole computer world is based off of them and if they were ever a way to figure out how to factor extremely large numbers quickly, the whole think would send us back to a non-electronic era since nothing would be secure.So is that stuff accurate?

I think you're a bit confused. Factorials and factoring are different things. Factorials are those silly exclamation points at the ends of numbers that you sometimes see: 5! == 5*4*3*2*1Factoring involves breaking down numbers into products of smaller numbers. Factoring is extremely important in cryptography. There are computer algorithms that factor numbers, and some are better than others, but the important thing is that it takes an extremely long amount of time to factor very large numbers. Modern encryption techniques use what are called "public keys" and "private keys." These are used in certain ways to turn messages into a coded message and to turn the coded message back. These keys are often related to each other by the factorization of a large number. The public keys are not kept secret and are transmitted but the private ones are not. So, if you could easily factor large numbers and you knew what algorithm a certain code was written in, you could use the public key to decode the private key pretty easily.Modern codes use the fact that it can take the average computer years and years to decompose large numbers into prime factors, so decoding complicated codes is often infeasible.Here's a more detailed explanation:http://www.cs.bham.a...public_key.html

[LongLiveYorke]

Dirtydutch, on Tuesday, April 15th, 2008, 4:15 AM, said:

A little word problem, to test Yorke's practical skills:If Dutch were to have unprotected sex with:1 girl with a .04% chance of being HIV-positive, one with a .002% chance, and a third with a 2% chance, statistically speaking, how likely would it be that I made it up?

Wait, three different girls? Yeah, it's made up.

[LongLiveYorke]

Okay, my turn.Let's say a friend comes up to me and gives me the following offer:He's going to put a certain amount of money in one envelope and twice that amount of money in another envelope. He then hands me one of the envelopes and lets me open it and see the amount of money inside. I do so. He then gives me the chance to switch envelopes. Should I switch or should I stay?Here's my solution:Well, there's clearly a 50/50 chance that I pick either the smaller one or the bigger one. So, if I switch, I could either double or half the money I have with a 50/50 probability. So, .5 * 2x + .5 * (1/2)x = 1.25xSince 1.25x > x, the amount of money I have, I should switch.But of course this solution makes no sense. Had I picked the other one, I would have come to the same conclusion and switched. What's the resolution?

[SuitedAces21]

chgocubs99, on Tuesday, April 15th, 2008, 2:40 AM, said:

Anyway, the point is that they talk about factorials in the book and how the whole computer world is based off of them and if they were ever a way to figure out how to factor extremely large numbers quickly, the whole think would send us back to a non-electronic era since nothing would be secure.

No more secrets, Marty.

[speedz99]

LongLiveYorke, on Tuesday, April 15th, 2008, 5:59 AM, said:

.5 * 2x + .5 * (1/2)x = 1.25xSince 1.25x > x, the amount of money I have, I should switch.But of course this solution makes no sense. Had I picked the other one, I would have come to the same conclusion and switched. What's the resolution?

Where do you get the '(1/2)x'? There are only two envelopes...'x' and '2x'. Adding in the '(1/2)' and halving that is what's giving you the extra .25.

SuitedAces21, on Tuesday, April 15th, 2008, 6:25 AM, said:

No more secrets, Marty.

I always read that in Kingsley's weird accent from the movie.

[JoeyJoJo]

Dirtydutch, on Tuesday, April 15th, 2008, 1:15 AM, said:

A little word problem, to test Yorke's practical skills:If Dutch were to have unprotected sex with:1 girl with a .04% chance of being HIV-positive, one with a .002% chance, and a third with a 2% chance, statistically speaking, how likely would it be that I made it up?

1 out of 4 girls between the ages of 14 and 19 have an STD.I learned that because April is STD Awareness month.

[ShakeZuma]

JoeyJoJo, on Tuesday, April 15th, 2008, 10:43 AM, said:

1 out of 4 girls between the ages of 14 and 19 have an STD.I learned that because April is STD Awareness month.

for some of us, every month is STD awareness month.

[hblask]

LongLiveYorke, on Tuesday, April 15th, 2008, 8:59 AM, said:

Okay, my turn.Let's say a friend comes up to me and gives me the following offer:He's going to put a certain amount of money in one envelope and twice that amount of money in another envelope. He then hands me one of the envelopes and lets me open it and see the amount of money inside. I do so. He then gives me the chance to switch envelopes. Should I switch or should I stay?Here's my solution:Well, there's clearly a 50/50 chance that I pick either the smaller one or the bigger one. So, if I switch, I could either double or half the money I have with a 50/50 probability. So, .5 * 2x + .5 * (1/2)x = 1.25xSince 1.25x > x, the amount of money I have, I should switch.But of course this solution makes no sense. Had I picked the other one, I would have come to the same conclusion and switched. What's the resolution?

First, this looks suspiciously like the Monty Hall problem.... so we need ground rules. First, we need to assume he hands you an envelope randomly (or let's you pick it randomly), and second, you have to assume that he *always* gives you the choice to switch regardless of which envelope you end up with.I think the problem is that the two X's are not the same. It's really:.5*2x + .5*(1/2)Y = ?? where x = .5Y.I haven't gotten the math to work yet, but I'm pretty sure it's something related to that....I'll keep looking at it.

[hblask]

OK, here's the answer.Let X be the amount in the larger envelope.Let Y be the amount in the smaller envelope.X = 2YSo, before we start, we haveEV = .5X + .5Y = .5(2Y) + .5Y = 1.5Y = .75X. This is as we expect. Our expected value is 50% more than the smaller envelope or 75% of the larger envelope.Now we pick one, but nobody knows which one it is. So our choice is:.5 (2Y) + .5 (.5X) = Y + .25X = Y + .25 (2Y) = Y + .5Y = 1.5Y or .75X, same as before.

[ShakeZuma]

JUST PICK A DAMN ENVELOPE

[Kaveros]

I have decided after reading this thread that LongLiveYork is a lot smarter than me.

[donk4life]

ShakeZuma, on Tuesday, April 15th, 2008, 10:40 AM, said:

JUST PICK A DAMN ENVELOPE

That's not logical.

[loogie]

speedz99, on Tuesday, April 15th, 2008, 7:31 AM, said:

Where do you get the '(1/2)x'? There are only two envelopes...'x' and '2x'. Adding in the '(1/2)' and halving that is what's giving you the extra .25.

I tried switching to 'x' from '(1/2)x', and I get the answer of 1.5x. SWITCH ENVELOPES IMMEDIATELY!

[JoeyJoJo]

ShakeZuma, on Tuesday, April 15th, 2008, 8:40 AM, said:

JUST PICK A DAMN ENVELOPE

When you have absolutely no ****ing clue what you're talking about, just keep your mouth shut. If it helps, think about losing $2k in equity in a free roll, the amount of absolute money we're talking about is irrelevant as our bank accounts are clearly not very similar. Thanks for chiming in with your words of wisdom.