Pls see 20 and 29.
I know. We have a math book that was my grandmother’s in elementary school. “Robinson’s Shorter Course Arithmetic”, published 1874. My husband is a Physicist, and he’s gobsmacked.
The first sentence of the “Suggestions To Teachers”section is “the instructor should not only fully understand it, in all its principles and details, but should also clearly perceive what particular faculties of the mind are concerned in its acquisition and use,”
Today’s teachers not only couldn’t do the math, but also couldn’t understand the sentence telling them how to understand the math. LOL!