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.
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.