We will understand in a practical way the principle of the equation.
Imagine that on a day at the table I see two fruits. But the next day I see a box and a fruit, and I know that the fruit on the table was not taken away. So the two fruits are there.
It seems easy to know that there is a fruit in the box. But if the number of fruits is very large, it is difficult to know.
But for that we make rules that facilitate us.
Try to follow.
On the left side what I saw yesterday. On the right side what I saw today. The number of fruits from yesterday is the same as today. Remember, something has to be the same for the equation to work.
Let's imagine that I took a fruit yesterday, so that fruit would not exist today. So how many fruits would be in the box? A fruit.
Imagine the same thing now, but now with balls. There were 5 balls on the table yesterday, and today I see a box and 3 balls. How many balls are in the box, it is easy to know that there are 2 balls in the box, but we have to follow the rules, then you will see why.
So yesterday I took 3 balls, so today I see only the box, so inside the box there are two balls.
Let's go again, yesterday I saw 35 stickers on the table, today I see a box and 15 stickers. If I take 15 stickers from yesterday, I get 20 stickers and today I see only the box, that is, there are 20 stickers inside the box.
Now I have 132 coins that I saw on the table yesterday, today I see a box and 52 coins. So yesterday I took the 52 coins, and today I see only the box, because I took the 52 coins out of 132, so we have 80 coins in the box.
If you don't understand, try watching again.