Here you go Fletch, whatever two digit number you pick and then subtract from to get your final number the total will always be
0,9,18,25,27,36,45,54,63,72 or 81 and they always have the same symbol next to each of these numbers. The entire list of symbols change each time you try again, but the same symbol will be next to 0 that is next to 9 and 18 etc....
Try it, pick 56 so you subtract 11 and get 45 which is in the list
pick 77 so you subtract 14 to get 63, again in the list
Your number will always be in the list and the symbols will always match.
Hope that helps.
Penguinfan