Ok here goes hope this makes sence: Every answer you come up with is a multiple of 9 ie: number 18 1+8+ 9 18-9 =9 number 45 4+5=9 45-9 = 36 Number 73 7 + 3 = 10 73 - 10 = 63 If you look at all the numers that are a multiples of 9 (9, 18, 27,36,45,54,63,72,81) they all have the same symbol The only reason the symbol chart changes each time you do it so you never get the same symbol twice. And there is your answer
I was going to say but then I don't want to be called a smart arse... The symbols change every time... do it with one number... then use a different one, but remember your previous number... when you look at the symbols you will see they are the same. It the calculation (that Tots Hope has kindly shown you) that does it as there are only a finite number of combinations it can be... and it's these numbers that have a particular (and repeated) symbol attached to them... Its why I love these mathematical conundrums cos they can have people going for ages, because they keep changing their number...
It freaked me out - now i just feel silly then thisis the girl that wrote her name on her gcse mathas exam and sat there and read a book through the exam!