Earlier in the week I read Evelyn Lamb’s review of David Reimer’s Count like an Egyptian and thought it would have many fun projects for the boys. Lamb’s review is here:

The first chapter is about multiplication and division. The book explains a procedure for multiplication which is (i) so interesting and (ii) so simple that I was stunned that I’d never seen it before.

We started with a simple example -> 9 x 7

Next we more on to see how this simple procedure could be applied to a slightly more complicated multiplication problem -> 34 x 51. After we calculated this product two different ways, I showed the boys how this Egyptian multiplication process was connected to representing the numbers in binary.

With these two examples out of the way, I wanted to see if the boys understood the procedure, so I had each of them work through an example on their own. First up, my younger son working through 13 x 19:

and the my older son working through 27 x 36:

I was happy to see that they understood the procedure and were able to work through examples on their own after seeing only two examples from me. That sort of gets back to my surprise at never having seen this idea previously. It really is a nice way to multiply, but also a nice way to sneak in a little arithmetic practice while learning some new math. Seems like a great project for kids.

I didn’t want to go too long this morning but I did want to show them that the procedure was also pretty easy to reverse. We’ll probably revisit the division algorithm next weekend, but here’s a quick look:

So, a fun project from the ideas in the first chapter of Count like an Egyptian. Happy to have seen Evelyn Lamb’s review of the book and really looking forward to several more projects based on the ideas in this book.

I’m glad I’m not the only one who was stunned that they’d never seen (or thought to invent) this multiplication method! In my math history class, we had a really interesting discussion about the advantages and disadvantages of this method versus the way most of us learn. One thing that a student pointed out was that the doubling method probably worked especially well with the Egyptian numeral system, which wasn’t a positional system. Memorizing a multiplication table would be at least as difficult as it is for us, maybe more so, but doubling would just require writing down the number twice and regrouping a few symbols (carrying the one).
I’m looking forward to seeing more of your kids going through this book!

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I’m glad I’m not the only one who was stunned that they’d never seen (or thought to invent) this multiplication method! In my math history class, we had a really interesting discussion about the advantages and disadvantages of this method versus the way most of us learn. One thing that a student pointed out was that the doubling method probably worked especially well with the Egyptian numeral system, which wasn’t a positional system. Memorizing a multiplication table would be at least as difficult as it is for us, maybe more so, but doubling would just require writing down the number twice and regrouping a few symbols (carrying the one).

I’m looking forward to seeing more of your kids going through this book!

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