Math Arguments

Error Analysis - Can You Be A Teacher, Too?

In a fascinating bit of testimony before a Michigan Senate Hearing, this slide was presented. The presenter (Dr. Ball) asked the legislators to identify where and how the 4th-grade solvers made their mistakes. 



David Wees asks:

"What is the mistake?"
"What is the thinking that led to this mistake?"

I saw both for (b) and (c) but the train of thought in (a) escaped me completely. What do you think happened in (a)?

What would you tell the students in each case?

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