When I was in college, I had an education professor show us the math books that Japan uses. They looked like comic books- same size and shape. They were written in strip form like comic books. They have one little comic book a year. That's all they use. (At least that was how this math series was written. I don't know if all Japanese math books are like this or just the one I saw.)
It was such a change from the big, chunky American math books. Obviously, Japan is doing something right.
Anyways, I saw this multiplication trick. It took me a minute to figure out what was happening in the pictures.
Here's how I think it goes:
For 13 x 12
Make a grid using the followign lines:
13: You draw two groups of vertical lines: 1 and 3.
12: You draw two groups of horitzonal lines: 1 and 2.
Draw 3 circles: 1 around the top left corner, 1 around the top right and the bottom left, and 1 around the bottom right corner.
Count how many intersection are in each circle. There should be 1 in the first, 5 in the second, and 6 in the third.
The answer is 156.
It only took me minute or so to do a couple of problems. Of course, I could probably do it in my head just as fast. However, it is a good trick to teach students to use when they can't use a calculator.
I'm trying to figure out how to do three or more digit numbers. Let me know if you know how.
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