Someone explain mathematics of this Mind Reader..

[FrostyBoy]

http://www.funnyjunk.com/pages/mindreader.htm

It's starting to scare me

[EPW]

I did it four times and it was wrong each time.

[civman2000]

A number minus the sum of its digits is always a multiple of nine. To see this, note that if, say, x=10n+m has two digits, x minus the sum of its digits is (10n+m)-(n+m)=9n; with more digits it is similar. Also, if x has only two digits, n is between 1 and 9, so the only possibilities are 9, 18, 27, 36, 45, 54, 63, 72, and 81. All of these numbers always have the same symbol; that's how it "reads your mind".

[Urban Ranger]

When you perform the operation, your remaining number is always a multiple of 9. If you look carefully, the same symbol appears at the slots (9, 18, 27, 36, etc.). However it changes randomly each "game."

Edit: civman2000

[Dis]

Originally posted by civman2000
A number minus the sum of its digits is always a multiple of nine. To see this, note that if, say, x=10n+m has two digits, x minus the sum of its digits is (10n+m)-(n+m)=9n; with more digits it is similar. Also, if x has only two digits, n is between 1 and 9, so the only possibilities are 9, 18, 27, 36, 45, 54, 63, 72, and 81. All of these numbers always have the same symbol; that's how it "reads your mind".

makes sense. Mine ended up being 9 (from 11).

and if it was really reading my mind, it would have showed a picture of a hot naked chick.

[Rufus T. Firefly]

Originally posted by civman2000
A number minus the sum of its digits is always a multiple of nine. To see this, note that if, say, x=10n+m has two digits, x minus the sum of its digits is (10n+m)-(n+m)=9n; with more digits it is similar. Also, if x has only two digits, n is between 1 and 9, so the only possibilities are 9, 18, 27, 36, 45, 54, 63, 72, and 81. All of these numbers always have the same symbol; that's how it "reads your mind".

Moreover, every time you click, it rearranges the symbols; first all teh multiples of 9 are a bell, then a cross, then a flower, etc. So you seem to keep finding different symbols that it "guesses." Pretty clever.

[FrostyBoy]

Originally posted by civman2000
A number minus the sum of its digits is always a multiple of nine. To see this, note that if, say, x=10n+m has two digits, x minus the sum of its digits is (10n+m)-(n+m)=9n; with more digits it is similar. Also, if x has only two digits, n is between 1 and 9, so the only possibilities are 9, 18, 27, 36, 45, 54, 63, 72, and 81. All of these numbers always have the same symbol; that's how it "reads your mind".

ah yes, now I remember the old trick, thanks!

[Dinner]

Originally posted by EPW
I did it four times and it was wrong each time.

Then you are very bad at math. Look at the board and choice multiple numbers, follow the instructions for each number you choose, and notice how no matter what number you choose if you add correctly they all have the same symbol next to them.

I'm not sure which mathamatical theorem they're using but no matter which number you choose the anwser will have the same symbol next to it.

[EPW]

Originally posted by Oerdin


Then you are very bad at math. Look at the board and choice multiple numbers, follow the instructions for each number you choose, and notice how no matter what number you choose if you add correctly they all have the same symbol next to them.

I'm not sure which mathamatical theorem they're using but no matter which number you choose the anwser will have the same symbol next to it.

lol perhaps