Here’s one from an assignment I am grading right now:

-4.9(2.55)^{2} + 25(2.55) + 3 = 92.61255

The thing on the left actually equals 34.8875. How did the student get 92.61255?

I’m tempted to say s/he forgot the minus sign in front of -4.9, but that would have given 98.61225 — same decimal part but different integer part. Maybe it’s a combination of dropping a minus sign and then writing down a “2” instead of an “8” in the ones place. I’m open to more systematic reasons; I’ll check in with the student Monday.

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Since the difference of 98.61225 and 92.61255 is 6, which is twice of 3, so it looks like s/he also flips of sign of 3

4.9(2.55)^2 + 25(2.55) – 3 = 92.61255