OK, thanks! At least now we have an answer to the "what went wrong?" question.
This was a case of an instructor assigning higher weight to a question that required more work (finding roots of a complex number), and then realizing that this was a bad idea due to the low success rate (since this was in an introductory linear algebra course with a sizable cohort of management students...)
By the time she changed the weights, some students were already on attempt 30 or 40!
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Changing problem weights after set closes
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