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Topic: say I flip a coin 100 times...
Replies: 46   Last Post: Apr 18, 2005 9:42 PM

 Messages: [ Previous | Next ]
 ken quirici Posts: 336 Registered: 1/29/05
Re: say I flip a coin 100 times...
Posted: Apr 13, 2005 8:41 AM

HERC777 wrote:
> and 1,000,000 other people all flip 100 coins themselves.
>
> on average, will someone flip the same 100 long sequence I did?
>
> how long a sequence will they match up to on average?
>
> Herc

There are 1M people and 100 coins. There are 2**100 possible
sequences of 100 coins. The chance that 1 out of the 1M will flip
the same sequence as you is (with ** indicating exponentiation)

1M * (2**-100) (if I remember correctly you add the
probabilities of independent events
to get the probability that they will
all occcur).

I don't know exactly what this is but its pretty small (certainly
less than 1 in 2).

For the second question:

The probability for matching the first 100 is above.
For matching the first 99 is 1M * (2**-99)
For matching the first 98 is 1M * (2**-98) (way less than 1)
.
.
.
For matching the first 1 is 1M * (2**-1) (way over 1)

So somewhere in between there:

For matching the first 20 is 1M * (2 **-20), or
around 1M / 1024000 (latter approximate) - slightly less than 1. So
around there.

I'm not sure of my logic here. I'm not sure about 1M * (2**-1). I
thought
probabilities only went up to 1?

Thanks.

Ken

Date Subject Author
4/12/05 HERC777
4/12/05 Jan Burse
4/12/05 HERC777
4/12/05 George Greene
4/13/05 Glenn C. Rhoads
4/13/05 Barb Knox
4/13/05 HERC777
4/13/05 Yajun
4/13/05 HERC777
4/13/05 Jay
4/13/05 HERC777
4/13/05 Jay
4/14/05 Yajun
4/14/05 George Greene
4/14/05 George Greene
4/13/05 Will Twentyman
4/13/05 briggs@encompasserve.org
4/13/05 briggs@encompasserve.org
4/14/05 George Greene
4/14/05 tchow@lsa.umich.edu
4/14/05 briggs@encompasserve.org
4/12/05 Tony
4/13/05 HERC777
4/13/05 ken quirici
4/13/05 Ralph Hartley
4/13/05 Robert Low
4/13/05 Ralph Hartley
4/13/05 Robert Low
4/13/05 tchow@lsa.umich.edu
4/13/05 HERC777
4/13/05 tchow@lsa.umich.edu
4/14/05 HERC777
4/14/05 George Greene
4/14/05 HERC777
4/15/05 tchow@lsa.umich.edu
4/15/05 tchow@lsa.umich.edu
4/16/05 George Greene
4/16/05 HERC777
4/17/05 George Greene
4/17/05 Patricia Shanahan
4/17/05 HERC777
4/18/05 Patricia Shanahan
4/17/05 tchow@lsa.umich.edu
4/18/05 HERC777
4/18/05 George Greene
4/18/05 tchow@lsa.umich.edu
4/18/05 HERC777