|
|
Nir Dahan Inner circle Munich, Germany 1390 Posts |
You have 999 dimes in a jar which are normal, and one dime which is 2 sided (both heads).
you now pick a coin at random from the jar and flip it 10 times. amazingly you got 10 heads in a row. what is the probability you are holding the 2 headed coin? N. |
landmark Inner circle within a triangle 5194 Posts |
Not sure on this, but I'll take a stab:
P( I pick a normal dime and it comes up heads 10 times) = (999/1000) x (1/2) ^10 So probability I picked the two headed coin = 1 - [(999/1000) x (1/2) ^ 10] = .99902. Hmmm, seems too high to me. Where is the mistake in my thinking? Jack Shalom
Click here to get Gerald Deutsch's Perverse Magic: The First Sixteen Years
All proceeds to Open Heart Magic charity. |
Nir Dahan Inner circle Munich, Germany 1390 Posts |
Jack there is indeed a mistake.
think bayes formula... |
Scott Cram Inner circle 2678 Posts |
Agreed. Relying on Bayesian probability is a mistake.
|
TomasB Inner circle Sweden 1144 Posts |
Could it be around half?
1 / (1 + 999 * 0.5^10) /Tomas |
Nir Dahan Inner circle Munich, Germany 1390 Posts |
Tomas got it! (again)
from a belly "feeling" it should be 50% since 1/1000 is almost as 1/(2^10) do we need the exact solution? |
Scott Cram Inner circle 2678 Posts |
If you can pick the coin out of the jar, and you're able to flip it, wouldn't you also be able to look at the coin itself? Why not just look on both sides? If it has no tail, you defintely have the coin! Otherwise, you don't.
|
Nir Dahan Inner circle Munich, Germany 1390 Posts |
Quote:
On 2007-01-31 12:44, Scott Cram wrote: scott com'on, do you also reason with other logical puzzles the way you did here? it would be no problem to devise a set of conditions that will limit the person from looking at both sides... this is a mathematical puzzle and should be solved that way. Nir |
TomasB Inner circle Sweden 1144 Posts |
I didn't use Bayes' though, but the definition of conditional probability: P(A|B) = P(A[union]B) / P(B)
/Tomas |
The Magic Cafe Forum Index » » Puzzle me this... » » 999 dimes (0 Likes) |
[ Top of Page ] |
All content & postings Copyright © 2001-2024 Steve Brooks. All Rights Reserved. This page was created in 0.02 seconds requiring 5 database queries. |
The views and comments expressed on The Magic Café are not necessarily those of The Magic Café, Steve Brooks, or Steve Brooks Magic. > Privacy Statement < |