The famous Simpson’s joke from when Bart goes to genius school:
Teacher at gifted school: So y = r^3/3 and if you determine the rate of change in this curve correctly, I think you will be pleasantly surprised.
Teacher: Don’t you get it, Bart? Derivative dy = 3r^2 dr/3, or r^2 dr, or r dr r. Har-de-har-har! Get it?