Let's do a 5/10 half-size example.

Good cards: 1,2,3,4,5
Bad cards:  a,b,c,d,e

First card drawn is 1
Good cards left:  2,3,4,5
Bad cards left:   a,b,c,d,e
Total cards left: 9

Now, for your second draw, there are 4 good cards left, and 9 total 
cards, so the chances of the next card drawn being good is 4/9.

Cards drawn:      1,2
Good cards left:  3,4,5
Bad cards left:   a,b,c,d,e
Total cards left: 8

Now, there are only 3 good cards left.  The chances of the next draw 
being good is 3/8.

Making more sense?

--Ben



Ian Skinner wrote:
> I'm sorry, but this is just bouncing off of my thick skull and getting lost 
> in space.
> 
> You've removed a "good" card from the possibilities.  For the first one, 
> there are 10 good cards and 20 total.  For the second, there are 9 good 
> cards and 19 total.  And so forth.
> 
> --Ben
> 
> How have you removed a good card if this is being calculated before any cards 
> are drawn?  Is this just the way of statistics?  
> 
> 
> --------------
> Ian Skinner
> Web Programmer
> BloodSource
> www.BloodSource.org
> Sacramento, CA
> 
> "C code. C code run. Run code run. Please!"
> - Cynthia Dunning
> 
> 
> 
> ...-----Original Message-----
> ...From: Ben Doom [mailto:[EMAIL PROTECTED]
> ...Sent: Friday, January 14, 2005 12:29 PM
> ...To: CF-Community
> ...Subject: Re: Calculating odds.
> ...
> ...You've removed a "good" card from the possibilities.  For the first one,
> ...there are 10 good cards and 20 total.  For the second, there are 9 good
> ...cards and 19 total.  And so forth.
> ...
> ...--Ben
> ...
> ...Ian Skinner wrote:
> ...> Draw 5 numbers from Set B = 10/20 * 9/19 * 8/18 * 7/17 * 6/16.
> ...>
> ...> Ok, I was going 10/20 * 10/19 * 10/18 * 10/17 * 10/16.
> ...>
> ...> Can you refresh my very rusty statistics on why both the numerator and
> ...denominator are reduced for each iteration?
> ...
> ...
> ...
> 
> 

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