 # Psychic .swf... how does it work?

http://mr-31238.mr.valuehost.co.uk/assets/Flash/psychic.swf

1. It does seem to matter if you think of a number first. Looking at a symbol is not sufficient.
2. Any time you do think of a number, it always gets the symbol exactly right. This has worked by any means of randomizing numbers I could try.
3. There is no input except for clicking on the crystal ball.

What’s going on here?

There are only 9 possible numbers, and they all have the same symbol.

Here’s an explanation I forwarded to a friend when I got forwarded this trick for about the 1000th time:

Simple algebra. Supposed your initial number is some 2-digit number, like ‘43’. This can be expressed as

10 * x + y where x is the “10s” digit and y is the “units” - in this case x = 4 and y = 3.

So then do what the instructions say - add up the digits: x + y. ( 4 + 3 = 7 )

Subtract from original number: (10 * x + y) - (x + y) = 10x + y - x - y = 9x. Or with the example 43: (10 * 4 + 3) - (4 + 3) = 10 * 4 + 3 - 4 - 3 = 10 * 4 - 4 = 9 * 4 = 36.

Therefore, the result is always some multiple of 9. On the chart, even though the symbols change from time to time, all the multiples of 9 have the same symbol, so the program can safely “guess” that you picked one of the multiples of 9 - 9, 18, 27 etc.

More specifically, anytime you perform the instructions (take a two-digit number, add the two digits, subtract that sum from the original two-digit number), you will always end up with a number that is evenly divisible by 9. In the list of symbols, all the numbers divisible by 9 have the same symbol, which is always the one that is the answer when you click.

Whoops, a little short there; there are 10 possible numbers (I forgot zero); they change the assignment of symbols every time so that you don’t catch on.

That’s genius. I was going to do the same number again, and when I looked at it, the symbols had changed!

Very funny.

ok

2 digit number: 25

2 + 5 = 7

25 - 7 = 18

18 is the flag, but it showed me the wrong symbol.

i think it checks and sees where your mouse is, i hovered over 18, then clicked the ball and of course it got it right then.

or did i do it wrong?

In general, when a “psychic” trick asks you to do some sort of arithmatic with the digits of a number, there’s usually something going on with multiples of nine. So even before I checked the math, I just looked at all of the multiples of 9 in the table.

Wow I must be a rube, it took me like 30 minutes to figure out how it worked.

Sigh…

Dad? Is that you? I told you to stop believing this shit.

Yes, you did it wrong.
It doesn’t know where your mouse is.
As has already been stated, the result of the arithmatic will always be divisible by 9.
All of the numbers divisible by 9 have the same symbol.
You were probably just looking at the wrong symbol before you clicked.

As was previously noted, if you have “x” in the 10’s place and “y” in the 1’s place, the result will be 9*x.

So you don’t even need to look at all the multiples of 9, or more calculation than 1 step: multiply your value of the 10’s place by 9.

All the symbols for the multiples of 9 are the same (except possibly for 90 and 99). Remember that the 10’s digit must be 1-9, so the largest multiple of 9 that needs to be represented is 81. So, 90 and 99 can be different, and it won’t change the results at all.

That is one of the funniest things I’ve read in a while! Beautiful!

I totally concur. I’ve been cracking up for 5 minutes.