Very OT: but fun

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Ran across this link . My
spyware/trojan/adware scanner does not ping so I think it's safe.
For those who don't like clicking on unknown URL's, it is a card trick. It
shows you six picture playing cards, king of hearts, jack of clubs etc. and
invites you to pick one. You then "click here". It then shows you five
playing cards and the one you picked is no longer there. And it works every
Would you believe that I could not work out how the trick was done? I looked
at the source code of page and was not enlightened, though I should have

I then thought I would ask the guys on aus. electronics if they could figure
out how it worked. You know, a fairly bright bunch who have never failed me
yet when I asked about something that was actually on topic.

Fortunately, before I made a complete moron of myself, I figured it out for
myself. I must have led a very sheltered internet life to be taken in for a
good fifteen minutes.
See below for how it works.

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The first .gif is of six picture cards. The second .gif is of five picture
cards, NONE of which are the same as the first six. So the one you picked is
not there but neither are any of the others. Duh.
Is this a case of "hiding in plain view" or "can't see the wood for the


Re: Very OT: but fun

OK, how do you think this "mind reading" game works....?


On Tue, 22 Nov 2005 22:16:59 GMT, "Peter Howard"

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Got it!

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Hmm, interesting one, Bob.
There are only nine possible answers. 9 and its multiples up to 81. All the
other numbers are there only to obscure the issue. The game fools people
like me by changing all the symbols in the chart every time you play.
However, 9,18,27--->81 always share the same symbol, whatever it is for the
particular round, which then comes up in the crystal ball.
It seems to work for three and four digit numbers too. Only a limited number
of answers, each one nine more than the previous one.
There must be a mathematical name for this phenomenon but I'm blowed if I
know what it is. I'm one of those unfortunates with a blind spot when it
comes to maths so I never went further than 10th grade Maths for Dummies.
I'm awestruck by people like Isaac Newton for instance, who invented
calculus with a quill pen by candle-light.


Re: Got it!

   You're doing better than me! I couldn't figure it out, so I
searched the net till I found the explanation. Well done!!
   There wouldn't be many people with the imagination and natural
mathematical skills of Newton, Charles Babbage or Alan Turing etc. I'm
definitely a very long way below that intellectual level. :)


On Wed, 23 Nov 2005 12:46:42 GMT, "Peter Howard"
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Re: Got it!

On Wed, 23 Nov 2005 12:46:42 GMT, "Peter Howard"

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It's called "algebra".

Let the number's digits be X and Y.

Therefore the number's value is 10X + Y

Result of subtraction is (10X + Y) - X - Y = 9X.

The possible values for your result are therefore 9, 18, 27, ..., 81.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

Re: Got it!

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Even Newton acknowledged the "giants" whose shoulders he stood on.
Where would he have been without that quill pen?

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