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Comment by madsushi | Hacker News Reader

Depends on if you're re-spinning between turns. Otherwise the first guy might get a 1/600 chance, but everyone afterward has better (or worse?) than 1/6 odds.

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Well, if it's the case that there's a 1/6000 chance that the first guy gets hit, it's 5999/6000 chance that the third guy gets it. (Not true, but it's gesturally correct).

So I imagine the odds are much less skewed or NOBODY forgets the spin between rounds. Also, if you don't spin between rounds and you're the 6th person to try it... this isn't really a game of risk anymore.

Why is the parent down voted? He was responding to the hypothetical case that the odds are initially 1/600 due to bullet weight and no one else spins.

Granted, he wrote 1/6000 instead of 1/600, but his basic point is correct: if no one else spins, the odds for each of the other 5 players would not remain ~1/6.

Thanks for the nudge! I did misread the hypothetical distribution the parent claimed. I definitely wrote that response in a hurry as a thought experiment to flesh out what the least bizarre rules for R.R. might be, but I was surprised by the vehement negative response.

Heh, you really have no idea of what you're talking about, do you? (Or are just plain stupid)

One, the other, or both might by true. However, in polite company there is rarely a need to ask the former and definitely not the latter.

Putting other people down, even or especially when they are wrong says more about you than them. Please don't.

I think he understands better than you, quite frankly.

Your odds never change, this is not how maths work. It's always 1/6, just like the odds of getting heads/tails in a coin flip is ALWAYS 1/2 no matter how many times you flipped already. Odds of receiving a certain outcome X number of times in a row can change,but the odds of a single event never,never,never do. Even if you flip a coin 10000 and got tails 10000 times, your 10001 flip also has a 50/50 chance of being heads or tails.

That's not how maths work. You're describing something that works for non-dependent events. Flipping a coin 50 times previously has no bearing on how it will flip the 51st time. The events are said to be independent.

In a six round revolver loaded with a single bullet and then randomized, pulling the trigger advances the next round. The first pull has a 1/6 (or 1/600, whatever) chance of firing. You will fire (assuming no mechanical malfunction and no randomization of the round after each pull) in those first 6 shots with a probability of 1.

Sorry, I honestly thought that you would spin before every try, in which case, every test would have the same 1/6 probability of firing.

Which just means you didn't read the comment to which you were replying...

I did, but because I didn't know that in Russian Roulette you are not supposed to spin before each try, I assumed that the guy I was replying to was wrong.

Simple misunderstanding that I made as well until I read your comment chain.

Im not sure you understand how a revolver works.

This is hacker news, chances are 1/6 he knows what a revolver is.

Revolver is a 1 in 6, but I say much higher he knows what a Desert Eagle or AWP is =). #CSDoesntStandForComputerScience

AWP lol.

Actually, it's 1/2 chance since it's either "yes" or "no".

Ahh, the freshman probability theorem. AKA the Lotto player's defense.

It's not just freshmen and lotto players. Sometimes it derails useful work:

http://www.thedailyshow.com/watch/thu-april-30-2009/large-ha...

Plus I'm feeling pretty lucky today, so how could I lose?

So the chance that I'm God is 1/2? Cool.

Ouch, looks like you are taking a lot of slack for this --- don't worry, I didn't realize the protocol for Russian Roulette was not to spin again after the first attempt, either. You're right if they spun it again afterwards, they are right if you just continue through the 6 bullet slots in the revolver.

Yeah, that's exactly what I thought, was really surprised by the number of down votes initially.

It's because you're underestimating the average intelligence of an HN reader. Basically everyone here knows how probability works for independent events.

He's saying that when it is first spun, the odds are low because of the weighting explained earlier. After that it is not re-spun and is instead advanced to the next bullet, which does change it, because you now are limiting the number of total possible places for the bullet.

I believe he meant that he first person has 1/6 (at least or most...idk) but assuming the next person goes there is one less chamber each time. 1/5, 1/4, etc. until you get to 1/1 at least. There would have to be some change between rounds to change that part.

Actually the chance of the 6th person getting the bullet is initially no greater than the chance that the nth person gets the bullet, since you have to take into account that the gun fires before the first person gets the gun, which happens to be 5/6.

> until you get to 1/1 at least

Possibly even more!

That is true with coin flips because the probability of a next coin toss coming up heads or tails is independent[0] of any previous coin tosses. Assuming you aren't spinning between turns, the probabilities are not independent anymore.

0: http://en.wikipedia.org/wiki/Independence_(probability_theor...

If you're not re-spinning between turns you're not doing independent trials like flipping a coin repeatedly.

Sorry, I honestly thought that you would spin before every try, in which case, every test would have the same 1/6 probability of firing.

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