A system of nonlinear equations is harder to solve than you think—and more of a puzzle than a math problem. Puzzles like this require you to look and find the one loose end you can pull to unravel the ...

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 ...