The Millennium Prize Problems are 7 math problems with a $1 million reward for solving them. Only one of them, the Poincare conjecture, is solved, and the other 6 are unsolved.
How would you rank them based on difficulty of understanding what the question is asking?
I’d say P vs NP is the easiest, Riemann hypothesis is understandable in the sense that its statement is not too technical, but understanding why it is important is another matter. NS smoothness is probably understandable to the average math or physics nerd who has seen some PDE’s. The rest require developing more machinery to even state the problems.
Maybe easiest to wrap your head around but certainly the hardest. Heh