## Friday, February 24, 2017

### If it's a math problem... do the math

Or, The Monty Hall problem: redux.

I recently posted a new video, addressing the Monty Hall problem. The problem is not the puzzle itself, which has been solved ad nauseam by everyone and their vlogbrother.

The video is about what information is. By working through the details of the Monty Hall puzzle, we can learn where information is revealed and how. That is the reason for the video; that and a plea for something so simple and yet so ignored that I'll repeat it again:

If it's a math problem, do the math.

Now, this may seem trivial, but math (and to some extent science, technology, and engineering, to say nothing of business, management, and economics) makes people uncomfortable, even people who say they "love math."

Hence the attempt to solve the problem with anything but computation. By waving hands and verbalizing (very error prone) or by creating similar problems that might be insightful (but mostly convince only those who already know the solution and understand it).

If all you're interested is the computations for the solution, they're here:

The point of the video is not this particular table; it's the insights about information on the path to it: how constraints to actions change probabilities and how those relate to information.

For example, from the viewpoint of the contestant, once she picks door 1 (thus giving Monty Hall a choice of door 2 and door 3 to open), the probability that Monty picks either door 2 or door 3 is precisely 1/2; that's calculated in the video, not assumed and not hand-waved. But, as the video then explains, that 50-50 probability isn't equally distributed across different states:

A final remark, from the video as well, is that by having computations one can avoid many time-wasters, who --- not having done any computations themselves and generally having a limited understanding of the whole state-event difference, which is essential to reasoning with conditional probabilities --- are now required to point out where they disagree with the computation, before moving forward with new "ideas."

If it's a math problem... do the math!