Despite the greatest strides in mathematics, these hard math problems remain unsolved. Take a crack at them yourself.

I’ve been out of school for decades, and I don’t spend my days solving equations (I’m more of a word person). Still, I like to think I have a solid grip on basic math: I can usually gauge whether a ...

There weren’t calculators or computers in medieval Europe. But there were math duels. Mathematicians would gather in public squares and pose tricky math problems to each other. Then they raced to ...