Hi, the theory goes as follows:
Let the two-digit number be: 10x + y. Now, adding the digits of the number we get: (x+y). Subtracting this from the two-digit number, we have: (10x + y) - (x + y) = 9x. Thus, taking any number arbitrarily, we will finally end up with multiples of 9, i.e., 0, 9, 18, 27, 36, 45, 63, 72, 81, 90, and so on.
Note that in the slide, all these numbers have the same symbol at any point in time. So, no matter what you choose, the crystal ball is always right as it will display the symbol corresponding to the same. :-D :-D :-D
Ensure there is a single line break between paragraphs.