how dows this work?

# Thread: how dows this work?

1. Junior Member
Join Date
Dec 1969
Posts
1

## how dows this work?

how does this know what number you are thinking of? try it and let me know http://www.vsisystems.com/numberboy.asp

2. Senior Member
Join Date
Dec 1969
Posts
10,852

## It doesn't.

It just knows that eight divided by two is four. It doesn&#039;t just work for 1 -25 ....It works for any integer, positive or negative.

3. Senior Member
Join Date
Dec 1969
Posts
10,852

## Here,,,,

1: Think of a number from 1 to 25.<BR>2: Double that number.<BR>3: Add 8.<BR>4: Divide by 2.<BR>5: Subtact your original number.<BR>6: The answer is four.<BR><BR>f(x) = ((( x + x ) + 8 ) / 2) - x<BR><BR>So...<BR><BR>f(x) - ((2x + 8) / 2) - x<BR><BR>So...<BR><BR>f(x) = (2x /2) + (8/2) - x<BR><BR>So...<BR><BR>f(x) = x + 4 - x<BR><BR>So....<BR><BR>F(x) = 4<BR><BR>Always.

4. Senior Member
Join Date
Dec 1969
Posts
10,852

## So...

It isn&#039;t a trick, it&#039;s just an illusion. A pretty stupid one at that, IMO. It doesn&#039;t even try to look impressive. There *are* some pretty good number teasers out there...Often that rely on psychology/sociology, or some esoteric mathmatical function to arrive at the solution. This one, on the other hand, just relies on the users having renounced formal education after the third grade. But I digress. All I really meant to say, is that I find this particular "puzzle" remarkably unsophisticated, so if you were planning on getting the source, and using it somewhere, you&#039;d be better off giving it a second thought, and finding something a little more worthwhile.<BR><BR><BR><BR><BR>

5. Senior Member
Join Date
Dec 1969
Posts
10,852

## The proof for where 8 is any rational number....

Step 1: Pick any rational number. -- f(x) = x<BR>Step 2: Double that number. -- f(x) = x + x <BR>Step 3: Add any rational number. -- f(x,y) = x + x + y<BR>Step 4: Divide the total by two. -- f(x,y) = (x + x + y) / 2<BR>Step 5: Subtract the original number. -- f(x,y) = ((x + x + y) / 2) - x<BR><BR>So, this can be reduced to:<BR><BR>First: f(x,y) = ((x + x + y) / 2) - x<BR><BR>Then: f(x,y) = ((2x + y) / 2) - x<BR><BR>Then: f(x,y) = x + (y / 2) - x<BR><BR>Then: f(x,y) = y / 2<BR>

6. Senior Member
Join Date
Dec 1969
Posts
10,852

## Stupid forum jacked up my formatting...

But you get the point.

7. Senior Member
Join Date
Dec 1969
Posts
96,118

## You spent all that time on SPAM

The dork who posted it just wanted you to visit his site. Notice the similarity between his username and the site name???<BR><BR>You wanna go kick yourself a while?<BR><BR>He got you...good.<BR><BR>

8. Senior Member
Join Date
Dec 1969
Posts
10,852

## Yep..I saw it...

After I had visited the site, anyway.<BR><BR>But...I decided to give him the benefit of the doubt.<BR><BR>Besides, the puzzle was so stupid, that deriding it publically was kinda cathartic.

9. Senior Member
Join Date
Dec 1969
Posts
96,118

## Heh...we used to use that one...

...or a variation of it...when I was in Cub Scouts. Let&#039;s see...that was...oh damned, I ran out of fingers, toes, and hairs on my head to count with. Well, so many years ago none of you were born.<BR><BR>

10. Senior Member
Join Date
Dec 1969
Posts
10,852

## Like I said in my reply...

....This one, on the other hand, just relies on the users having renounced formal education after the third grade. <BR><BR>Perfect for cub scouts. &#060;Grin /&#062;

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