Morgan Stanley Traders Lost $390 Million in One Day in August

[IluvVol]

Quote from Capablanca:

Let's see. What is the ratio between 1/6 and 1/3? Same as 1/3 to 2/3. Do you understand why that is pertinent to the given example and the Wikipedia explanation? Probably not.

As for any supposed mental diarrhea on my part I'm sure anyone who has taken basic Statistics can understand the point I was making which is the same reason I could at least understand the rationale behind batman28's answer. That you do not even seem to recognize the method being employed tells me enough about your own qualifications to judge my answers.

I have studied basic statistics, probabilities, measure theory, stochastic calculus on a masters and PHD level and guess what.... I also dont understand your reasoning. Nobody cares about Batman28's rationale because it was/is/will be wrong and he refused to admit either. Your probabilities given were wrong. They are 1/3 and 2/3 as simple as that. The question was simply does it make sense to switch or not to switch. Some offered to add to that the chances of winning when switching and not switching and those you got DEFINITELY wrong. I mean what do you lose by admitting you were wrong??? I am stunned by this arrogance. You make yourself look like a complete idiot by continuing to attack others who understood the subject matter, explained it to you a multiple times and you still insist on them being wrong.

Here is something for you: You know what the title says? I paraphrase: "Monty Hall problem is a typical example of 'cognitive illusion' often used to demonstrate people's resistance and deficiency in dealing with uncertainty."

I would definitely say this applies to you and this is not being rude but a logical conclusion from the sum of your previous posts. Here you go:

http://ist-socrates.berkeley.edu/~fitelson/148/krauss.pdf

But hey, a lot of PhD got this initially wrong when this puzzle surfaced for the first time long time ago......being incorrect is excused......however..................stupidity to insist on something that is now proven wrong ..........is not!!!

 

[Equalizer]

Quote from volpri:

If these dudes can lose like that, in spite of having the best equipment ...smartest minds....etc ...where is the hope for a peep squeak like me?

Actually a peep squeak like you has a huge advantage, due to being a peep squeak. You don't need to delever a multi-billion dolar portfolio because:
a). You are not that highly levered where compared to these guys
b). You don't have a multi-billion dollar portfolio under management.
c). Your portfolio composition can vary significantly because you can buy and sell securities that these guys can never consider due to their relative liquidity.

Of course, the above assumes you actually know what you are doing.

What you need to realise if you work with this sheah is that models are just that, models of reality! Hearing that idiot Viniar talk about "25 sigma events" makes me want to slap his big fat head!

 

[joeb8822]

Not sure but does Nick leeson work there ??

Realizing the gravity of his situation, Leeson left a note reading "I'm Sorry" and fled on February 23. Losses eventually reached £827 million (US$1.4 billion), twice the bank's available trading capital. After a failed bailout attempt, Barings was declared insolvent on February 26. 1995


Rogue Trader

great movie for traders to watch

 

[IluvVol]

Quote from Equalizer:

Actually a peep squeak like you has a huge advantage, due to being a peep squeak. You don't need to delever a multi-billion dolar portfolio because:
a). You are not that highly levered where compared to these guys
b). You don't have a multi-billion dollar portfolio under management.
c). Your portfolio composition can vary significantly because you can buy and sell securities that these guys can never consider due to their relative liquidity.

Of course, the above assumes you actually know what you are doing.

What you need to realise if you work with this sheah is that models are just that, models of reality! Hearing that idiot Viniar talk about "25 sigma events" makes me want to slap his big fat head!

Lol, 25 sigma is nuclear worldwar, nothing else ;-)

 

[ptunic]

I have to say I was initially fooled and thought the probability was 50% regardless of if you switched or not, after the new information (of a cup being removing, knowing that that particular cup did not have the coin). I clicked on the link to play the game and still didn't understand it for a while, even after playing about 10 times. It took me about 5 minutes of thinking to figure it out.

Finally I figured it out. The perspective I had to do was to mentally separate out the 3 cups into a set of 2 distinct groups.

Group 1: my original choice (which may or may not contain the coin)

Group 2: the 2 cups that I didn't choose

So let's take two cases.

Case 1: the coin is in Group 1 (under the cup I choose)

Case 2: the coin is in Group 2 (under one of the other two cups)

Now let's assign probabilities to these two cases -- before the interviewer removes a cup.

Case 1 : 1/3
Case 2 : 2/3

Now the interviewer removes a cup. By definition, the cup the interviewer removes has to be from Group 2.

Let's start backward. Let's assume Case 2 (the coin is in Group 2). Then the interviewer has no choice but to remove the cup in Group 2 that doesn't have the coin, and thus by definition of Group 2, the remaining cup is guaranteed to have the coin. Thus, in Case 2, the probability is 100% if you choose the switch, and 0% if you choose your original cup.

Now let's move on to Case 1. In case 1, your probability if you choose the switch (Group 2), is 0%. Your probability in Case 1 if you choose the same cup as originally selected is 100%.

So let's put this info together:

If you switch, here is your probability of guessing correctly:

Case 1: 1/3 chance of occurring * 0% = 0%
Case 2: 2/3 chance of occurring * 100% = 2/3
Sum = 0% + 2/3 = 2/3 chance

What if you always choose your original?

Case 1: 1/3 chance of occurring * 100% = 1/3
Case 2: 2/3 chance of occurring * 0% = 0%
Sum = 1/3 + 0% = 1/3

Thus you improve your odds from 1/3 to 2/3 if you switch your choice. Fascinating stuff


edit: fixed typos with extra 2/3

 

[Capablanca]

Quote from IluvVol:

I have studied basic statistics, probabilities, measure theory, stochastic calculus on a masters and PHD level and guess what.... I also dont understand your reasoning. Nobody cares about Batman28's rationale because it was/is/will be wrong and he refused to admit either. Your probabilities given were wrong. They are 1/3 and 2/3 as simple as that. The question was simply does it make sense to switch or not to switch. Some offered to add to that the chances of winning when switching and not switching and those you got DEFINITELY wrong. I mean what do you lose by admitting you were wrong??? I am stunned by this arrogance. You make yourself look like a complete idiot by continuing to attack others who understood the subject matter, explained it to you a multiple times and you still insist on them being wrong.

Here is something for you: You know what the title says? I paraphrase: "Monty Hall problem is a typical example of 'cognitive illusion' often used to demonstrate people's resistance and deficiency in dealing with uncertainty."

I would definitely say this applies to you and this is not being rude but a logical conclusion from the sum of your previous posts. Here you go:

http://ist-socrates.berkeley.edu/~fitelson/148/krauss.pdf

But hey, a lot of PhD got this initially wrong when this puzzle surfaced for the first time long time ago......being incorrect is excused......however..................stupidity to insist on something that is now proven wrong ..........is not!!!

Make a decision tree and calculate the probabilities at each stage. It will work out as I have stated. This is elementary stuff.

The source of the difference in our answers is we are answering two different questions. The calculations I am presenting involves the entire process. The ratios you and GTS are insisting on are the ones you are left with once other options have been excluded.

Looking at the entire decision tree, enumerating all possible outcomes, the probability of choosing the correct cup and sticking with it is 1/6. This and the scenario where one chooses the correct cup but switches are (if I recall the term and definition correctly) mutually exclusive. Once one option is chosen the other is no longer available. Similarly for the other branch where it works out to 1/3. So in the last stage you are comparing a probability of 1/6 from the outset to a probability of 1/3 from the outset. If you only look at that last stage in isolation and no longer count the other possibilites that have been previously eliminated then one can look at the 1/6 vs. 1/3 as a 1/3 probability versus a 2/3 probability since the other 50% of probabilities have been previously eliminated so that explains your answer of 2/3.

It should be noted therefore that I agree with the statistical implication that it pays to switch and thus differ from Batman28 on that point. Still when he mentions a calculation involving 16.666% I know where he's coming from, unlike let's say you and GTS who apparently don't. If you need a reference to know the pertinence of these calculations just look at the discussion page of the Wiki article previously cited.

Does this require further explanation?

 

[IluvVol]

Quote from Capablanca:

The source of the difference in our answers is we are answering two different questions. [/B]

There is no different questions you moron. There is one puzzle, one interview question, and one correct answer. All you did in your previous posts was NOT answering the question asked or answering it incorrectly. Your last posts elaborates on what GTS recommended LONG TIME AGO (a decision tree) and copies ideas other posters made long before you, would you have read those posts. So, finally you agree with our answer. Good!!!

 

[jrlvnv]

After working this problem over and over again and reading this thread WAY to many times, I admit that you are right and I was wrong. I have no shame in admitting it, problem lies in admitting your wrong when you swear up and down your right. It wasn't till the 10 cup example came about till the light bulb went off. TaDAAAAA... ring the bell monty. This was by far the best thread I read here in awhile.

IluvVol.. grats on all your math studies...... Maybe this will give me the kick in the ass needed to finish up my school instead of being bent over a card table for the rest of my life.

Thanks to everyone that explained it in a moron's language so I can understand

Quote from IluvVol:

I have studied basic statistics, probabilities, measure theory, stochastic calculus on a masters and PHD level and guess what.... I also dont understand your reasoning. Nobody cares about Batman28's rationale because it was/is/will be wrong and he refused to admit either. Your probabilities given were wrong. They are 1/3 and 2/3 as simple as that. The question was simply does it make sense to switch or not to switch. Some offered to add to that the chances of winning when switching and not switching and those you got DEFINITELY wrong. I mean what do you lose by admitting you were wrong??? I am stunned by this arrogance. You make yourself look like a complete idiot by continuing to attack others who understood the subject matter, explained it to you a multiple times and you still insist on them being wrong.

Here is something for you: You know what the title says? I paraphrase: "Monty Hall problem is a typical example of 'cognitive illusion' often used to demonstrate people's resistance and deficiency in dealing with uncertainty."

I would definitely say this applies to you and this is not being rude but a logical conclusion from the sum of your previous posts. Here you go:

http://ist-socrates.berkeley.edu/~fitelson/148/krauss.pdf

But hey, a lot of PhD got this initially wrong when this puzzle surfaced for the first time long time ago......being incorrect is excused......however..................stupidity to insist on something that is now proven wrong ..........is not!!!

 

[IluvVol]

Quote from jrlvnv:

After working this problem over and over again and reading this thread WAY to many times, I admit that you are right and I was wrong. I have no shame in admitting it, problem lies in admitting your wrong when you swear up and down your right. It wasn't till the 10 cup example came about till the light bulb went off. TaDAAAAA... ring the bell monty. This was by far the best thread I read here in awhile.

IluvVol.. grats on all your math studies...... Maybe this will give me the kick in the ass needed to finish up my school instead of being bent over a card table for the rest of my life.

Thanks to everyone that explained it in a moron's language so I can understand

No worries, I also play poker a lot! ;-)

 

[Capablanca]

Create a decision tree and use it to solve this problem. That should make things self-explanatory.