Magic mind reading ~ seeking decryption ~

I'll tell you slowly ..

Why not choose 12? 1+2=3? 12-3=9? If 13 is selected, 1+3=4? 13-4 or 9? Shall we start with 14... 14-5 or 9?

20, 20-2= 18? ... how to subtract 20 from 29? Both terms add up to 18. ......

If it is 30 (I won't give an example ...), the subtraction is all 27.

40 is 36? 50 is 45? 60 is 54? 70 is 63? 80 is 72? 90 is 8 1.

It tells you to choose between 10 and 99. No matter which one you choose, the addition and subtraction of the two terms are the 9 numbers (9? 18? 27? 36? 45? 54? 63? 72? 8 1)

Do you understand a little?

Here comes the point. ........

As long as the symbols of these nine numbers are the same, it knows that no matter which one you choose, because the symbols of its nine numbers are the same.

So it knows which number you chose. .....

That card, I don't know ... Unfortunately. .......

Maybe the other answers are right. .......