Harv wrote; >THEY made a silly error due to thoughtlessness at the time.
Sorry Harv, but I disagree. Even if students admit to making a "silly error" a teacher who is truly using student responses to assess students understanding would use this information as diagnostic to determine what mis-understanding the student has that would allow this type of error. This is obviously a student who does not understand the "concept" of division when it is stated in that way. More assessment would need to be done to see if the student understands division in other circumstances, to determine if it needs to be addressed.
Students who know what they are doing will not make this error no matter how silly they are being because they will recognize that it does not make sense. Just as they would correct themselves when they mis-read the word read in a sentence such as "I only read that story once." They automatically correct themselves as soon as they recognized that the answer they arrived at was nonsensical. If they do not auto-correct that is the first clue that they do not realize that the answer did not make sense. Then an aware teacher would follow up with checking to find out how deep the misunderstanding goes so that they can provide the experiences that will allow the student to gain an understanding.
Moving on at the point where a student is having this misunderstanding and attributing it to laziness or lack of motivation is a common response for teachers that are unaware of what they are seeing.
Bottom line, it is inconceivable to me that students who 'could' do accurate computation would 'refuse' to do so for any reason.