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I think the temptation I have is to call this a “careless” mistake and urge more practice. Let’s probe deeper.

1. What does this kid know and understand about exponents?

2. What’s the fastest way to help?

3. What makes this mistake so tempting?

Thanks to Sadie Estrella for the awesome addition to our ever-mounting pile of exponents mistakes.


Bob Lochel writes:

“I used this question as part of a benchmark assessment given to over 1,100 students at our high school, as preparation for the state test.  Only 14% of students gave the correct answer B, while 66% of students chose A as their response.  I’m not surprised that students would perform weakly on a domain/range question, but I am surprised that so many chose A.  I featured this problem as a set-up for a domain and range activity on my blog:, but feel free to share it with the mathmistakes crowd.”

So, what do we think about choosing A? Any theories?