RE: Calculating odds.

[Ian Skinner]

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?


--------------
Ian Skinner
Web Programmer
BloodSource
www.BloodSource.org
Sacramento, CA

"C code. C code run. Run code run. Please!"
- Cynthia Dunning



...-----Original Message-----
...From: Won Lee [mailto:[EMAIL PROTECTED]
...Sent: Friday, January 14, 2005 12:14 PM
...To: CF-Community
...Subject: Re: Calculating odds.
...
...Ian Skinner wrote:
...> I am panning the general high intelligence of this group.
...>
...> Say you have a set of 10 numbers that is a subset of a set of 20.
...>
...> If you where to draw 5 numbers from the set of twenty, but can only
...draw any given number once, what are the odds of all 5 numbers picked
...being in the set of 10?
...>
...
...Distinct numbers?  You have to be more specific.
...
...Set A {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20}
...Set B {1,2,3,4,5,6,7,8,9,10}
...
...Draw 5 numbers from Set B = 10/20 * 9/19 * 8/18 * 7/17 * 6/16.
...
...
...> My quick answer was .5^5 = 0.03125, or 1 in 32, but I realized those
...odds would only apply if you could pick any number in all the draws, so
...you could have {1 1 1 1 1}, right?
...>
...> My second guess was that it might be 1/2*10/19*5/9*10/17*5/6 =
...0.071666093337919963306960210984979, or ~1 in 14, but is that correct?
...Or does whether a previous draw is in the subset of 10 or not matter?
...>
...> This unfortunately exhausted my current knowledge of statistics it just
...has been way too many years/decades.
...>
...>
...> --------------
...> Ian Skinner
...> Web Programmer
...> BloodSource
...> www.BloodSource.org
...> Sacramento, CA
...>
...> "C code. C code run. Run code run. Please!"
...> - Cynthia Dunning
...>
...> Confidentiality Notice:  This message including any
...> attachments is for the sole use of the intended
...> recipient(s) and may contain confidential and privileged
...> information. Any unauthorized review, use, disclosure or
...> distribution is prohibited. If you are not the
...> intended recipient, please contact the sender and
...> delete any copies of this message.
...>
...>
...>
...>
...
...

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