difficult problem

There are intuitive problems, just apply a common calculation to find the answer, but on the contrary, many problems ask trick questions, making many people unable to think of the

This problem is relatively harmful to the brain, but it is extremely easy to think of!

How to connect 9 points together with only 4 adjacent strokes - the puzzle only 20% of the respondents solved.

Can you overcome obstacles to challenge humanity's most transcendent wisdoms for nearly three centuries?

A banker in the US will give a million dollars to the successful winner of a problem that mathematicians have not found an answer since the 1980s.