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Re: why do buses always come in 3s? , math book?
Posted:
May 27, 2000 12:06 PM
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prezky@apple.com says...
> Don McDonald <dsmc@actrix.gen.nz> wrote:
[Mean lowest number in a 40-choose-6 lotto game]
> > > = 41/7
> >
> > =?? (N+1) / (L+1). ??
> > is this correct.?
[snip]
> > possible argument about beads on a necklace.
> Yes, how does it go again?
Isn't it something like this:
The N numbers represent gaps between N+1 beads on a string. Choosing L
numbers from N without replacement corresponds one-to-one to choosing a
way of colouring the N+1 beads with L+1 colours, with at least one bead
of each colour (since without replacement), and then stringing them on
the string so that colours are contiguous and in a particular order. (The
gap between two beads of different colours represents a lotto number.)
The mean value of the lowest number equals the mean number of beads of
the first colour (or any colour), and that's easy to work out.
Have I got that right?
James Lawry.
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