RE: [GZG] [OT] Probability formula needed

I'm pretty rusty.  Let's see.

Assuming the 7 objects are unique, I think the odds of getting all right
are 1 in 7 factorial ("7 Permutations 7").

You can't get 6 right without 7, of course.

To get 5 right, multiply 1 in 7 factorial by the number of ways you can
pick 2 of the 7 ("7 choose 2" or 7 factorial divided by (7-2) factorial
times 2 factorial).

To get 4 right, multiply 1 in 7 factorial by the number of ways you can
pick 3 of the 7 ("7 choose 3") then by the number of ways you can juggle
3 items in three slots with none correct (Gut says 2, but I'm not sure
of the underlying math for larger numbers.  For 4, I think it's 9.)

> -----Original Message-----
> From: gzg-l-bounces@lists.csua.berkeley.edu [mailto:gzg-l-
> bounces@lists.csua.berkeley.edu] On Behalf Of Allan Goodall
> Sent: Thursday, November 17, 2005 9:45 AM
> To: gzg-l@lists.csua.berkeley.edu
> Subject: [GZG] [OT] Probability formula needed
> 
> Hi, folks.
> 
> This is a bit off topic, but may be of general interest to the folks
> on the list. I'm posting here because this is the place I'd most
> likely expect to see an answer!
> 
> I need a probability formula. The situation is as follows:
> 
> You have 7 objects owned by 7 people. If you were to randomly guess
> which person owns which object, what is the probability that you would
> guess all 7 objects correctly? Guess 5 out of 7 correctly? Guess 4 out
> of 7 correctly?
> 
> Instead of just the answers, I'd prefer the actual probability
> formula. It's been decades since I studied probability theory. A link
> to a web site with probability formulas would be good, too (and would
> be on topic for a gaming list! *grin*).
> 
> Any help would be appreciated!
> 
> Allan
> --
> Allan Goodall 	   http://www.hyperbear.com
> agoodall@hyperbear.com
> awgoodall@gmail.com
> 
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