On Thu, 16 Dec 1999, Doug Kaufman wrote:
> On Thu, 16 Dec 1999, Philip Webb wrote:
> > 991215 Klaus Weide calculated: 
> > > Let's say there are 20 temp files existing & kept track of by Lynx
> > > at any one time, realistic with source_cache, UI pages, downloads.
> > > What are the chances that, among 20 filenames drawn out of 10000
> > > (with repetition),  >= 2 are the same?  I get: approximately 190/10000.
> > 
> > not "approximately", exactly (grin): 1 + 2 + ... + 19 .
> 
> I am not sure which algorithm you are using to approximate this. The
> exact probability is:
> 
> 1 - (9999! / (9980! * 10E76))

For this I get

   0.018832767068024059

(by just multiplying 0.9999 * 0.9998 * ... * 0.9981, then subtracting from
1.  Your expression makes it look more complicated than it is.)

So we do have approximately the same result.  
(But thanks to Doug we have a formula instead of just a gut feeling...)

   Klaus

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