I think differential equations are a funny example because they range from "turning a crank" to solve some simple ones to a very difficult search for a combination of clever hacks and techniques from a large and poorly organized toolbox... e.g., there's a lot of questions over whether the typical undergrad course in differential equations is well organized.
Most of the human brain's energy consumption is not dependent on how hard you are thinking
https://cordis.europa.eu/article/id/442230-can-you-burn-calo...
I think differential equations are a funny example because they range from "turning a crank" to solve some simple ones to a very difficult search for a combination of clever hacks and techniques from a large and poorly organized toolbox... e.g., there's a lot of questions over whether the typical undergrad course in differential equations is well organized.