[Avernar]

I remember reading about an ELI5: The "Old Math" in Tom Lehrer's New Math. That post was funny.

If you haven't heard the song, he describes the way they used to do math as follows:

Consider the following subtraction problem, which I will put up here: 342 minus 173. Now, remember how we used to do that:

Three from two is nine, carry the one, and if you're under 35 or went to a private school, you say seven from three is six, but if you're over 35 and went to a public school, you say eight from four is six ...and carry the one, so we have 169.