xin chào i found this--->

That. Someone explained to me how it works. Every time the symbols change, but all the possible các câu trả lời have the same symbol so it will always be right.

Look:

21. 2+1=3. 21-3=18.
66. 6+6=12. 66-12=54.
72. 7+2=9. 72-9=63.
10. 1+0=1. 10-1=9.
52. 5+2=7. 52-7=45.

On the chart, all those numbers have the same symbol. Keep doing it with any other number, on the same chart (without clicking the ball), and the symbols will be the same.

That's how it works.

Oh wow....AHH IT BURNS...VIRUSES...D: