Lattice Method Multiplication

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Another strategy for multi-digit multiplication, great for visual learners.

If you're a student watching this... after you've finished the video, try the problems below. Watch BOTH examples, because the 3digit x 2digit one will REALLY help you. The first example is just to show you how it works.
1. 421 x 38
2. 537 x 213
3. 4567 x 123
4. 1234567 x 89
When you've done the problems, put them through your calculator and be AMAZED at how easy it was to find success!

For teachers: The lattice method dates WAY back, first documented in an early Italian math book, printed in 1478! And it's older than that, since the base-10 system originated in India, and was used by Fibonacci in the 13th century! COOL! By the way, I don't think Fibonacci used this method. I looked at a translation of his book Liber Abaci (Book of Methods), and I couldn't find it in there. I DID find something interesting though. Fibonacci demonstrates a version of the standard algorithm. It was done as an inversion of what we do now! Biggest number on bottom line, number you are multiplying by above that, answer on top line! Fun. Don't try that at home, kids, it's 800 years out of date!

Anyway, Lattice method lets visual learners find success. More box-filling, and a cunning diagonal addition strategy brings success. It also lets you keep to single digit multiplication. I have seen students who draw a blank with other methods really gel with this one.

I demonstrate it with rectangular boxes for the lattice so that the products are recognisable. Everywhere else I've seen it, it's done with square boxes. For visual students, they may go blank at this presentation and be unable to get it, because they just can't see the digits AS the products. I'm like this too - it requires conscious effort. The rectangular accommodation should see them take to it easily.
CC: by ME!