Short Rectangular Multiplication
Grandma Knows Best
I had a bit of an unusual childhood, I spent a lot of time at my grandmother's house, which was in a very rural part of New Hampshire. Since there wasn't a lot to do, and because my grandmother was a schoolteacher in a one-room schoolhouse, I spend a lot of time learning things. Due to the lack of other activities my grandmother had taught me to read and write and do basic arithmetic by the time I was three years old.(And to think, if we only had TV at the time)
I always found my grandmother's house exciting, because she would have all of these interesting books lying around. There was a big thing at the time called programmed learning, and I loved thumbing through those books and picking up what I could.
What I find most intriguing, however, were the things my grandmother taught me that you just don't learn in school anymore. One of these things was short rectangular multiplication. Now realize that this is what I called it because of the way it was done, this may not be the technical term for it. It does however, seem to be a lost technology, that was once caught in a one-room schoolhouse and only occasionally shows up these days as a math trick, with no apparent use.
What is it and How is it Done
Now the lost technique is a great way to multiply eight or nine digit numbers by hand. These days anybody who multiplied eight or nine digit numbers by hand would be considered insane. While this number would probably be too big to be displayed on an inexpensive calculator, if somebody had to multiply the numbers, they would find a way and it probably wouldn't be to do it manually. I sometimes actually enjoy doing large problems with this technique, but it's just a challenge to see if I'm focused. To describe how it's done would be very awkward, so I have some videos that I made for a website I started to build called How to Math Videos, and these will probably show it far better than I could explain in writing. The actual website never really got off the ground because in my attempt at saving money, I choose the only Web host that was incapable of uploading videos, but that's another story.
Short Rectangular Multiplication Demonstrated
More examples are avaliable here
- How to Math Videos
A site I started in attempt to help students with Math. I will probably get back to it one day but it takes a lot of time and the project is too big, so it will have to wait until my finances are in order enough to allow me to work on it.
Now with the advent of calculators, this technique is pretty obsolete. But the point is that there are lots of interesting things that have been taught in the past, that are virtually unknown today. My grandmother taught me a lot of these, but just think of the incredible amount of knowledge that has been known in the past, but isn't remembered today. Much of it might be obsolete, like short rectangular multiplication, but some of it could possibly have a great impact on the world today, if it was only known. So I'd like to say, just because something has been long forgotten, doesn't mean that it is useless. If you absolutely had to multiply two ten digit numbers together, and you couldn't find a calculator anywhere, you might be glad that you knew short rectangular multiplication.
The Math Doctor
- RAH Successes -- Home The Math Doctor
GreenMathDR is one of the founders of The Math Doctor Tutoring Service in Glendale California.