He showed his son an interesting mathematical trick, he surprised his teacher with it and received an A.

Oh, how I love various math tricks, puzzles and logic puzzles! And even more I love to show them to my son. Now he is finishing 9th grade and it is not surprising that his favorite subject at school has always been mathematics.

I recently I learned a new mathematical trick with numbers, which of course I shared with my son, who surprised his math teacher with it and got an A.. The trick itself is very simple, but at the same time quite effective, and now I will demonstrate it to you.

And so, for this trick we only need a sheet of paper and a pen or marker.

We write on paper a four-digit number that needs to be guessed in advance (I'll tell you why later). For example, let's take the number 5325.

Now we ask your opponent (the one you want to surprise, let it be some inveterate mathematician) to write absolutely any four-digit number below. For example, he will write the number 2413 (I will write down my opponent's numbers in red marker).

After that, below we once again write a four-digit number. This time I'll write down the number 7586.

Then we ask our opponent to write again any number (only a four-digit one), continuing to write down in a column. Suppose this time he writes the number 6724.

After that, we just have to write one more last number. I will write the number 3275.

And now the fun part! We tell our opponent that we knew in advance the answer to this example (the number that will be obtained by adding all these numbers) and this number is written on a piece of paper that lies in our pocket. We show a piece of paper with the answer and see the number 25323 on it (you can check it on the calculator).

What is the secret of this mathematical trick?

And the secret of this trick is actually very simple. We write down the answer and the first number in advance, and all subsequent numbers are written down according to this algorithm. Our opponent really writes down random four-digit numbers, but we are picking up such a number, so that when two numbers are added together, the number 9 is obtained (when two four-digit numbers are added, the number 9999). To make it clearer, watch a short video below..

We carry out a similar operation with the last pair of numbers, the sum of which will also be equal to 9999.

Thus, the sum of all these numbers will be as follows: we subtract 2 from the first number 5325 and add it to the beginning. The result is the number 25323!