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# Friday math movie - NUMB3RS and Bayes’ Theorem

By Murray Bourne, 23 Nov 2007

There are 2 related videos for your viewing pleasure this week.

Here's Charlie (the main character in the NUMB3RS tv series) explaining the Monty Hall problem to his students. It has a good twist, of course. What you expect intuitively is not the best decision.

Here is another explanation of the same thing from Ron Clarke (which has a bit of a Monty Python feel):

## Baye's Theorem

Here's quite a good (if lengthy) explanation of Bayes' Theorem. From the page's intro:

... an excruciatingly gentle introduction.

There's a bunch of Java applets on that page that let you play with the concepts and investigate the meaning.

### 5 Comments on “Friday math movie - NUMB3RS and Bayes’ Theorem”

1. Darmok says:

Cool videos; I love the Monty Hall problem!

P.S. It should be “Bayes’ theorem”; it’s named after Thomas Bayes.

2. Murray says:

Doh - thanks, Darmok. Yes, I knew it was Bayes apostrophe - but after years of typing 'apostrophe s', it kinda becomes a habit.

I have corrected it in the post.

3. maria says:

Iam going to put a link to this information. I saw this Numb3ers episode last weeK and I enjoy. Thanks.

4. isah says:

that's interesting Charlie!

5. Richard says:

I disagree with the usage of Bayes Theorem to solve the Monty Hall problems.

If there are 3 choices, you pick 1 of the 3 (1/3 probability being the same as 2/6 probability), and the host removes 1 of the other 2 options (1/3 probability being the same as 2/6 probability), then, 1/2 (50%, being 1/6) from the choice removed by the host should be transferred to your selection, and the other 1/2 probability (likewise 50%, being 1/6) should be transferred to the other option that you may or may not switch to.

At that point the 2 remaining selections (yours, originally 2/6, now plus the 1/6 from the removed option, being 3/6, which is the same as 1/2 or 50%) is equal to the other option (originally 2/6, now plus the 1/6 from the removed option, being 3/6, which is also the same as 1/2 or 50%).

So, to me, you are now positioned at 50:50 (3/6 v. 3/6), and not 2/3 to 1/3. Consequently, you have an even probability of selecting a car/goat in the Monty Hall/NUMB3RS video example, and not a 2:1 probability as most of these videos state as fact.

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