The kid’s handwriting is hard to read, so I want to point you towards 9 times 13, near the top of this page.

I think that this is a great example of a mistake that you can feel fairly good about. Your thoughts, on any of his work?

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- Post author By mpershan
- Post date October 22, 2013
- 4 Comments on 9 times 13 is 121

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- Post author By mpershan
- Post date September 4, 2013
- 1 Comment on More Numbers and Operations in Base 10

Any idea what’s going on here? In case fuzziness is an issue, the question is “What is the biggest multiplication that you know without thinking very much about it?”

Also, I anticipate getting some flack for the wording of this question being potentially confusing. I don’t disagree, necessarily, but I want to offer a partial defense of the question. First, I had been reading the TERC curriculum and they make a point of not saying “multiplication facts,” instead always saying “multiplication combinations.” I haven’t wrapped my head around what makes sense to me, so I punted on the question, figuring that I’d be there to help kids figure out what it meant. And I did, and everybody else offered answers that made sense. Most importantly, the question served it’s purpose: some kids wrote “8 x 8” while others wrote “1,000,000,000,000,000,000 x 10.”

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- Post author By mpershan
- Post date June 25, 2013
- 2 Comments on Multiplication Shortcut Fail

- What exactly is the shortcut?
- Why does this shortcut seem reasonable?
- We’d all agree, I think, that 2 x 6 = 26 is not a result of this kid not understanding what multiplication is. I’ve made that mistake before, and I bet that you have too. So, why is it a common mistake? What does this say about how a mind works while working on math?

[Any advice on how to tag this, CCSS-wise?]

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- Post author By mpershan
- Post date May 3, 2013
- 14 Comments on Lattice versus Partial Products

I’d love to hear anything that you’re thinking about this in the comments.

I wonder: should we be giving kids explicit guides for these sorts of algorithms at all? Algorithms ought to be patterns in thought. Does a mistake like this begin to make a case against these sort of printed aids?

Thanks to Professor Triangleman for the submission.

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- Post author By mpershan
- Post date January 6, 2013
- 3 Comments on Multiplication Algorithm

- Post author By mpershan
- Post date October 31, 2012
- 7 Comments on Area of Walls

What’s the mistake? How can you help the kid?

When you’re done with this post, go check out Mary Dooms’ blog and go follow her on twitter. Thanks for the submission, Mary!

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- Post author By mpershan
- Post date August 1, 2012
- 2 Comments on Khan Academy: Meaning of Multiplication