Lots of good stuff going on here. But I don’t think I entirely understand where 1/8 came from, though I get how that gets turned into 5.8.
[I never know whether to include all the mistakes from a class set or just a few. I feel as if it's helpful to include more mistakes, but sometimes overwhelming. My solution today is to post one especially cool mistake largely, and the others smallerly. Let me know whether that works.]
How did the student get from 0.8 times 1.6 to 8.0?
What tendency is this an example of? (Or is the mistake unique to the context?)
How would you test your theories?
Thanks to Chris Robinson for the work.
What strikes me about this piece of student work is how clean and predictable their mistake is.
Is this sort of mistake the rule or the exception? Does a mistake like this reflect the fact that many/most student errors are due to coherent mental models, or is it the rarer exception in a world dominated by stormy minds that fling ideas at math less predictably?
Thanks again to Dionn!
How did the student make the decision to plot 1/4? Tell a story.
Source: Chris Robinson
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!
No, Sal Khan did not actually submit this question. But Andyhav3 asks:
What’s this student getting at with “the right side of the decimal,” and how might you help Andyhav3?
[Click here to see how your approach compares to how his question was actually handled.]