Why is 2+5=9?

Matchstick puzzles have always captivated people's curiosity and challenged them. The following puzzle was introduced by Arsenii Nikolaiev, a former silver medalist at the International Mathematical Olympiad.

Nikolaiev sent the puzzle to many students at top universities, but even those who were good at mathematics often couldn't find the answer.

This is a familiar type of math problem, not too difficult, but it still stumps many people. Comment with your solution and see how many people think the same way as you.

Hieu Lam

Source: https://vtcnews.vn/vi-sao-2-5-9-ar905808.html