Only 1% of people answered correctly within 10 seconds

Calculate to find the number behind the question mark. There is a secret rule hidden behind the numbers, be careful to find that rule to solve this question.

Does this question stump you?

Let me tell you that most players answer this question wrongly because of haste. So please stay calm to be able to give the correct result.

Quickly register yourself in the top smartest people by leaving your answer in the comment box!

Trung Temple

Source: https://vtc.vn/chi-1-nguoi-tra-loi-dung-trong-10-giay-ar832700.html