To avoid direct reference to the quiz, I abstracted the question like this:
Overall dev set error:20%
Errors due to incorrectly labeled data: 5%
Errors due to other reason: 15%
Question: it is true that if we fix the incorrectly labeled data we will reduce the overall dev set error to 15%?
I think the answer should be True. Because fixing labeled data is different than fixing other reasons (like image quality, etc.). In this case, there is no overlap that some error is due to both mislabeled data AND other reasons (other wise the overall dev set error would not match the sum of all the reasons). The hint says it is an estimation of a “ceiling”, but in my opinion, by fixing the label in dev set, it is guaranteed that those 5% would be reduced to 0%, and the overall error would be 15%.
What am I missing here?