Those books immediately came to mind when I saw the submission title. In my opinion Dirk Gently's Holistic Detective Agency is Adams's best work.
Oh, you don't need math for this. Try moving a sofa with my wife instead. I think fate/god/the universe/whatever designed some problems that are impossible to solve so that couples never run out of things to fight about
PIVOT!
Wow, I would like to see some animations of doing this for sofas going up and over the railings and down stairs. It works better with the sofa upside down.
From the linked video, it sounds like there isn’t one. He says that some of the constants used in the equations defining the various curves don’t have a closed form.
This is my favorite "easily explainable to someone who doesn't know math but still very interesting" problem.