As a college chem professor, the reason for this is nearly always cheating.
"Hmm, you got the right answer with the wrong method, and your friend that you sit next to every day used the right method and got the same exact answer as you, down to the rounding? Haha, what are the odds??!?"
Zero. The odds are zero (within sig figs).
I tried this in university. I knew the right answer but not how to get it, so I made a "mistake" in the calcs. It was circled with "something's not right". No marks.
Conversely, when I was in college I once did all of the work right for a math problem that took two whole pages to do. And then I copied the wrong number to the answer line. But they saw my work and saw the right answer written down, so they only took like one point off of a 15 point problem or something like that.
I did the same. Forgot the formula but I explained how I would have solved the problem if I rememberd the formula. I think I got like 2/10 on the question lol
We had a formula once that you could aproach from two ways. So I went backwards once I couldn't figure out how to continue. In the end I still didn't know how to get from x to y but this was a small enough step the corrector would know surely.
"...and after I completed the formula, I used my calculator to get the answer."
