My Algebra 1 kids taught me lattice multiplication the other day. I'd seen it before but never understood it. I gave my tablet to a girl during class and said, "Teach me." It took her a little convincing to make her believe me, but then she did it.

This is my old-school version of multiplication on the left with Kaitlin's lattice multiplication on the right. I was skeptical that it would always work, but in breaking down what goes where and what gets combined with what, it does work. The sad thing is that the kids don't really get why it works. Lattice multiplication doesn't show the place values that you're using - at least in such an obvious way, I guess.

Oh well. I'm just happy that they can multiply! (On paper. I'd like to keep the other kind of multiplication out of the classroom. Though I did find out last week that I have a student expecting sometime this year.)

## 3 comments:

That is awesome! If I have time later I will fool around with it to try and figure out how it works...

Have you seen this? I proved algebraically that it works, but it still kind of seems like magic.

That's cool! Never seen that before. I'll have to play with it tomorrow and see how it works.

Kinda reminds me of the finger trick for trig & remembering values on the unit circle.

Thanks!

we teach that in the Math for Liberal Arts classes. Look up Napier's bones. here: http://en.wikipedia.org/wiki/Napier's_bones

Google it to get pictures.

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