You are Here: Home >< Maths

# Daniel Tammet on the Late Show with David Letterman

1. Towards the end of this video, Tammet tells Letterman his date of birth. Letterman acts like he's trying to figure out the day, and guesses (?) Wednesday - and he's right!

There are 2 possibilities: Letterman made a lucky guess or he had looked up Tammet's birth-date and day before the show. What is the probability that Letterman made a lucky guess?

Is that correct?
2. There's a 1 in 7 chance. There are 7 days per week. So the probability of randomly picking the correct one is 1/7.

Due to the nature of the show, it's likely there was a script or a plan, so Letterman probably did not guess.
3. (Original post by Llewellyn)
There's a 1 in 7 chance. There are 7 days per week. So the probability of randomly picking the correct one is 1/7.
While that's true, that's not what I asked. My question was: Given that we know that Letterman got it right, what is the probability that he guessed?

Towards the end of this video, Tammet tells Letterman his date of birth. Letterman acts like he's trying to figure out the day, and guesses (?) Wednesday - and he's right!

There are 2 possibilities: Letterman made a lucky guess or he had looked up Tammet's birth-date and day before the show. What is the probability that Letterman made a lucky guess?

Is that correct?
I got the same answer as you. But I'm no expert.

(Original post by Llewellyn)
There's a 1 in 7 chance. There are 7 days per week. So the probability of randomly picking the correct one is 1/7.

Due to the nature of the show, it's likely there was a script or a plan, so Letterman probably did not guess.
1/7 is P(Correct | Guess) but the OP is asking for P(Guess | Correct).

(This is all assuming that the initial probability that Letterman took a lucky guess is the same as the initial probability that he cheated).
While that's true, that's not what I asked. My question was: Given that we know that Letterman got it right, what is the probability that he guessed?
You are assuming that the probability of guessing is 1/2 or 0.5 . How do you know that this is true? No evidence has been given to suggest this.
6. (Original post by Llewellyn)
You are assuming that the probability of guessing is 1/2 or 0.5 . How do you know that this is true? No evidence has been given to suggest this.
It's an assumption made by thomaskurian. While it may not be true, you can still do the maths.
7. (Original post by Llewellyn)
You are assuming that the probability of guessing is 1/2 or 0.5 . How do you know that this is true? No evidence has been given to suggest this.
I think you have a point.
8. (Original post by notnek)
It's an assumption made by thomaskurian. While it may not be true, you can still do the maths.
I would have preferred him to have stated that the general answer is where p is the probability that Letterman guessed.

Stating your assumptions is vital, especially in Statistics.
9. (Original post by Llewellyn)
I would have preferred him to have stated that the general answer is where p is the probability that Letterman guessed.

Stating your assumptions is vital, especially in Statistics.
p is not the probability that Letterman guessed. (We are trying to find that out.) p is the probability that Letterman guesses in such situations.
p is not the probability that Letterman guessed. (We are trying to find that out.) p is the probability that Letterman guesses in such situations.
p is the probability that Letterman guessed before any additional information is given. You're trying to use this to work out the probability that Letterman guessed once we know that his answer was correct.

Is this what you meant? I didn't really understand your post.
p is not the probability that Letterman guessed. (We are trying to find that out.) p is the probability that Letterman guesses in such situations.
Yes but you don't know the probability that Letterman guessed or the probability that letterman guesses in such situations. Don't you see the problem?

Analogy:
2y = x
Find x without knowing what y is.
12. (Original post by Llewellyn)
Yes but you don't know the probability that Letterman guessed or the probability that letterman guesses in such situations. Don't you see the problem?

Analogy:
2y = x
Find x without knowing what y is.
I thought Llewellyn described it fine:

P(Guess)=p
14. (Original post by notnek)
I thought Llewwellyn described it fine:

P(Guess)=p
He said that p is the probability that Letterman guessed. If that were true, our answer would be p.
He said that p is the probability that Letterman guessed. If that were true, our answer would be p.
No, our answer would be p/ (7-6p), because you want to find the probability that he guessed given that he got it correct.

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: July 12, 2012
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### A-level exams coming up?

Find everything you need here.

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams