I have legitimately met college students in the last few years who had no frame of reference for how much time they should be putting in. Freshmen who think that spending 15 minutes a week looking over their notes is "studying a lot" are pretty common right now (in the USA).
Three hours of study for each hour spent in class is an average estimate of what it takes to absorb even moderately difficult material in courses in sci/tech.
Relevant quote: "Every truth has four corners. As a teacher I give you one corner, and it is for you to find the other three." (Confucius)
Which with napkin math can be shown to be bullshit. Students are spending approximately 1/3 of their time in classes, so how would they get time to sleep among the 4/3 required by studies and classes?
1:3 hours sounds super aspirational even for only the hardest of classes like organic chemistry and fluid dynamics.
But your napkin calc isn't addressing the bit where you only take 1-2 classes like that per semester and pad the rest out with things like literature and electives so you could have a life.
