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## Bizarre multiplication

A while ago I wrote this post about multiplication. In it I explored a few different ways of multiplying and what I felt worked best and why. I covered the main ones, and I realise there are many different methods.

However, today, while marking my year 8 books I discovered a method I had never seen before:

I looked at it and thought, “bizarre”. I asked the girl in question who taught her it and she said she’d didn’t know, but that it made sense to her but grid and column methods don’t.

I like the method, it reminds me of expanding a pair of binomial brackets, but it the numbers were 19 + 4 etc. It’s fantastic for 2 digit by 2 digital or 2 digit by 3 digit and I think it shows the distributive property quite well. There are major limitations though. It looks really neat in these two examples, but the questions that were 3 digit by 3 digit were a little spaghetti like and the ones with 4 digits were totally illegible.

Have you seen this method before? Do you like it? I’d love to know!

Categories: #MTBoS, Commentary, Maths, Strange
1. June 17, 2014 at 10:44 pm

I have seen it before (maybe just the once though) – just as you suggest, like the “claw method” for double brackets. It utilises the same partitioning and separate multiplications that the grid method, but doesn’t lay it out in as clear a manner. I’d suggest it is perfect to use as a mental method, but if you have a piece of paper to work on, then there are more reliable methods to choose from.

2. June 17, 2014 at 10:50 pm

(A mental method for 2-digit times 2-digit numbers, maybe 3 and 3 if you have an accurate memory for multiple things.)

3. June 18, 2014 at 1:52 am

I think it’s just a messy partial product scheme. Like http://bit.ly/1lx3PJP, but written out with distribution lines instead of listed. I like partial products because they emphasize place value and fit well with teaching estimation, and can lead to more subtle strategies. The distribution lines are a nice touch, though, and probably a good transition to algebra.

1. June 20, 2016 at 3:31 pm