Daniel Tammet on the Late Show with David Letterman

Maths and statistics discussion, revision, exam and homework help.

This thread is sponsored by:
Announcements Posted on
Important: please read these guidelines before posting about exams on The Student Room 28-04-2013
Sign in to Reply
  1. thomaskurian89's Avatar
    • Exalted and Worshipped Member
    Daniel Tammet on the Late Show with David Letterman


    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?

    P(\text{guess}|\text{correct})= \frac{P(\text{guess}\cap\text{co  rrect})}{P(\text{correct})}

    =\frac{1/2*1/7}{1/2*1/7+1/2*1}

    =\frac18

    Is that correct?
    Last edited by thomaskurian89; 12-07-2012 at 15:06.
  2. Llewellyn's Avatar
    • Section Moderator
    • Astray anyway
    Re: Daniel Tammet on the Late Show with David Letterman
    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. thomaskurian89's Avatar
    • Exalted and Worshipped Member
    Re: Daniel Tammet on the Late Show with David Letterman
    (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?
    Last edited by thomaskurian89; 12-07-2012 at 16:28.
  4. notnek's Avatar
    • TSR Demigod
    • Location: Bangkok, Thailand
    Re: Daniel Tammet on the Late Show with David Letterman
    (Original post by thomaskurian89)


    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?

    P(\text{guess}|\text{correct})= \frac{P(\text{guess}\cap\text{co  rrect})}{P(\text{correct})}

    =\frac{1/2*1/7}{1/2*1/7+1/2*1}

    =\frac18

    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).
    Last edited by notnek; 12-07-2012 at 16:29.
  5. Llewellyn's Avatar
    • Section Moderator
    • Astray anyway
    Re: Daniel Tammet on the Late Show with David Letterman
    (Original post by thomaskurian89)
    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. notnek's Avatar
    • TSR Demigod
    • Location: Bangkok, Thailand
    Re: Daniel Tammet on the Late Show with David Letterman
    (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. thomaskurian89's Avatar
    • Exalted and Worshipped Member
    Re: Daniel Tammet on the Late Show with David Letterman
    (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. Llewellyn's Avatar
    • Section Moderator
    • Astray anyway
    Re: Daniel Tammet on the Late Show with David Letterman
    (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 \frac{p}{7-6p} where p is the probability that Letterman guessed.

    Stating your assumptions is vital, especially in Statistics.
  9. thomaskurian89's Avatar
    • Exalted and Worshipped Member
    Re: Daniel Tammet on the Late Show with David Letterman
    (Original post by Llewellyn)
    I would have preferred him to have stated that the general answer is \frac{p}{7-6p} 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.
  10. notnek's Avatar
    • TSR Demigod
    • Location: Bangkok, Thailand
    Re: Daniel Tammet on the Late Show with David Letterman
    (Original post by thomaskurian89)
    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.
  11. Llewellyn's Avatar
    • Section Moderator
    • Astray anyway
    Re: Daniel Tammet on the Late Show with David Letterman
    (Original post by thomaskurian89)
    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. thomaskurian89's Avatar
    • Exalted and Worshipped Member
    Re: Daniel Tammet on the Late Show with David Letterman
    (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 agree that my answer was wrong and your answer is correct. It's just that you incorrectly described the symbol p you used in your answer.
  13. notnek's Avatar
    • TSR Demigod
    • Location: Bangkok, Thailand
    Re: Daniel Tammet on the Late Show with David Letterman
    (Original post by thomaskurian89)
    I agree that my answer was wrong and your answer is correct. It's just that you incorrectly described the symbol p you used in your answer.
    I thought Llewellyn described it fine:

    P(Guess)=p
    Last edited by notnek; 12-07-2012 at 17:52.
  14. thomaskurian89's Avatar
    • Exalted and Worshipped Member
    Re: Daniel Tammet on the Late Show with David Letterman
    (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.
  15. Llewellyn's Avatar
    • Section Moderator
    • Astray anyway
    Re: Daniel Tammet on the Late Show with David Letterman
    (Original post by thomaskurian89)
    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.
Sign in to Reply
Share this discussion:  
Article updates
Moderators

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

Reputation gems:
The Reputation gems seen here indicate how well reputed the user is, red gem indicate negative reputation and green indicates a good rep.
Post rating score:
These scores show if a post has been positively or negatively rated by our members.