Algebra and Calculus are more or less "solved." Unless by algebra, you mean abstract algebra... but the open questions there tend to be quite esoteric. That s

Algebra and Calculus are more or less "solved." Unless by algebra, you mean abstract algebra... but the open questions there tend to be quite esoteric. That said, we did recently see a novel approach to solving quadratic equations ( https://www.sciencealert.com/math-genius-finally-discovers-easy-way-to-solve-quadratic-equations-after-4-000-years https://www.sciencealert.com/math-genius-finally-discovers-e... ). I'd say that HN posts a lot of quanta articles, and quanta has a "bias" towards results that can be explained to a semi-lay audience. You really don't want to know enough about modular elliptic curves to understand Wiles' proof of Fermat's conjecture. But sometimes number theory proofs come up here too.