This trick annoys me!
 

How does this work any programmers out there, do the choose a double digit number and the rat whateva he is will guess your symbol everytime.

On the third go i chose 66 and im sure he brought up the wrong symbol :hmm:

Probably didn't

http://www.learnenglish.org.uk/games...er-central.swf

Ahh... not my own words im to :88) -

Was told this: The symbols rotate each time you try it, so the symbol will be different each time. It seems that no matter the number you end up with is dividable by 9.
Count from zero, every ninth number has the same symbol.

Don't get on the grounds he got all 10 in a row wrong. :-?

Indeed. Easy to prove. You take some random two-digit number. We can represent that as:
a * 10 + b
where a and b are natural numbers from 0 to 9.

Then, the second number is the sum of those digits:
a + b

Finally, you subtract the second from the first:
(a*10 + b) - (a + b) = a*9

Given that a is a natural number smaller than 10, it's pretty obvious that this has to be a multiple of 9, at most 81.

Ha he got them all wrong.

You use the result of the subtraction, not your original number. So if you pick 40, you do 40 - (4+0) = 36 and then look 36 up on the symbol list. Lo, 36 is a multiple of 9.