What is the principle of "guessing the heart"

The requirements of this mind-reading game are

The magical mind-reading handed down by gypsies. It can measure your inner feelings.

Choose a two-digit number at will (in other words, choose a number from 10~99 at will), add the ten digits of this number to the four digits, and then subtract the sum from the selected number.

For example, if you choose 23, then 2+3=5, and then 23-5= 18.

Find the number corresponding to the last number in the chart, remember this number, and then click the crystal ball. You will find that the figure displayed in the crystal ball is the one you just remembered in your mind.

Suppose the number you choose is XY, then

The end result is

10*X

+

Y

-

(X+Y)= 1

9*X

That is to say, no matter you choose you, the final result must be a multiple of 9, that is, 9, 18, 27, 36, 45, 54, 63, 72, 8 1.

One of them. Every time you click, the number corresponding to each number will change once, giving you the illusion that the answer is uncertain, but no matter how the number corresponding to the number changes, the number corresponding to 9 18, 27, 36, 45, 54, 63, 72, 8 1 is the same. So of course what you think is displayed, because no matter what number XY you choose, it will be the answer.