I suspect lots of people here have little or no higher education. Mine was 10+ years ago, so an occasional refresher can be nice; I remember the general concepts, but not necessarily the details.
The category of Things I Once Knew but Have Since Forgotten because I Don't Them Often Enough probably includes 95+% of everything I've ever learned about both mathematics and computers/programming.
The people on here who rattle off the names of various mathematical theorems like it's nothing and act like it's weird not to remember how intro-level algorithms work without thinking really hard and doing some trial-and-error for a while or consulting a reference must have much more interesting jobs than I ever have. :-/
US universities with ABET-accredited programs teach 1's/2's complement to freshman EE/CpE majors in a first course on digital logic, which typical doesn't have any prerequisites.