Mailing List Archive: 49091 messages

## [REBOL] Re: A Rebol Challenge. The Monty Hall Puzzle

### From: nitsch-lists:netcologne at: 18-Dec-2001 0:41

```
RE: [REBOL] Re: A Rebol Challenge.  The Monty Hall Puzzle

[carl--cybercraft--co--nz] wrote:
> On 17-Dec-01, Carl Read wrote:
>
> > Here's a fixed version...
>
> > rebol[]k: s: 0 r: func[n][random n]m: does[p: r 3 c: r 3 p = c] loop
> > 10000 [if m[k: k + 1]if not m[s: s + 1]]print ["Kept" k "Switched"
> > s]
>
> > Nowhere near as short as some of the other posts, but anyway, here's
> > my reasoning behind it...
>
> > The prize is placed behind one of 3 doors...
>
> >    prize: random 3
>
> > You choose one of the doors...
>
> >    chosen: random 3
>
> > Now, Monty can see if they're a match - ie, if you've picked a
> > winner...
>
> >    matched?: prize = chosen
>
> > Which returns true if you've chosen the prize. If you decide to keep
> > this then it's obvious (I hope:) that you had 1 chance in 3 of
> > picking the prize.
>
> > But what if you accept Monty's offer to switch?  Well, there's only
> > two posibilities:
>
> > 1) You'd chosen the prize, so switching from that means you lose
> > regardless of what Monty does.
>
> > 2) You hadn't chosen the prize, Monty exposes the other losing door,
> > and so you switch to the winning door.
>
> > So a switch always means a reversal of your original choice - a
> > winning choice becoming a losing one and vice-versa.  So...
>
> >    matched?: not matched?
>
> > But what happens to the "1 chance in 3 of picking the prize."? Well
> > that also means you had 2 chances in 3 of losing, right? And the
> > switch makes an original loss a win, so switching gives you 2
> > chances in 3 of winning, thus doubling your chances of a win.
>
> After showing the above explaination to someone (not on this list)
> they still didn't believe it, so I've written a graphical version in
> the hope that pictures will win out where words fail...  (Not a View
> version though - run it from the Console.)
>

well, thats to complicated to me, i give up.
i have a 2/3 choice to get a priceless door, this chances are
better, and so i want to be priceless.
hey, and if i hit, Monty will show me the other priceless door!
so i have two :)

happy without a price
-Volker ;-)
```