This reminds me of a much more reasonable bad teacher from my childhood, which I still remember as unfair

We had been learning the vowels, which in one thing were listed as a, e, i, o, u, and sometimes y, among others with the just the five most common ones

So days later when we had a quiz my answer to which letters are vowels was a, e, i, o, u, and sometimes y. I got a red x, with "and sometimes y" crossed out. I don't think we were given points but it felt like zero points.

I wonder if this is an actual child being taught not to trust questions or someone implementing the idea of get internet points by typing a question, writing a childlike a correct answer, then writing in pen a bad teacher response

When I was in elementary, my teacher said that "Lutetia" was how the Romans called the city of Liege. As an avid reader of Asterix comics, I knew this isn't true and corrected her and said it was the Roman name of Paris. She insisted that it is Liege. Anyway, the next day, she came back to class and said that she looked it up and that I was indeed correct and Lutetia referred to Paris and gave me a chocolate bar and told me to keep reading comics. Good teacher.

Why would you ask "How is this possible" when you expect the answer to be "it's not"?

The teacher is fucking stupid. The question says Marty ate more, that is not only possible it is a given.

Take that to the principal, stupid teachers shouldn't teach

If you state that Marty ate more as part of the question, you cannot answer in any other way, because it denies mathematical logic here. You introduced a lie as part of the problem, and if I need to decide myself which part of the statement is a lie, I can pick whatever I want, let's say, Marty didn't ate 4/6, but 6/6. This teacher should be taken to the gulag.

It is entirely possible and his answer was correct. Question was phrased incorrectly, if the teacher wanted an answer "it is not possible" he should have said both pizzas were the same size.

The teacher is the one who's confused here. The kid is entirely correct.

I... Um... I've been looking at this for a minute and I can't tell why the answer is unconventional, nor what the fuck the teacher is on about.

Given 4/6 x > 5/6 y therefore x > 5/4 y

Marty's Pizza must have been more than a quarter larger than Luis'. The kid is exactly right.

And the teacher is not flexible enough to engage outside their expectations for how the question was supposed to be answered.

Clearly the expectation was for the kids to take the unstated assumption that the two pizzas were of the same size, and reject the premise as unreasonable (note the heading "Reasonableness").

Teachers that don't accept an unexpected but true answer are not teaching. The test taker had a correct take, one of the pizzas could be bigger than the other. It was not specified in the question. I am so glad I am out of school

i can't fathom this being real, most probably this was made for karma farming or something.

This brings back memories of when I realized that I was smarter than most of my teachers.

This is bizarre. The info provided in the question was that Marty ate more than Luis, the question was how would that be possible given that Marty ate 4/6 of his while Luis ate 5/6 of his. The answer the kid wrote (Marty's pizza was bigger than Luis') is the only possible correct answer.

The grader is asserting that the information given in the question was wrong and that "actually it was Luis who ate more pizza"--even though it stated as a premise that "Marty ate more". How are you supposed to give a correct answer on a test if you are expected to accept one premise (proportion of pizzas eaten) while disregarding another premise (Marty ate more than Luis)? How do you decide which part to disregard? Would they have accepted the answer, "Luis actually only ate 3/6 of his pizza, not 5/6)"? Wouldn't that be just as valid an answer as "Marty actually didn't eat more than Luis"?

Some real "steel is heavier than feathers" energy coming off this teacher.

The title of this post is disappointing. The given answer is sound and it seems safe to assume it was arrived at by thinking mathematically.

"This is not possible because..."

This kid is never going to trust teachers again.

He was right. The question is not even worded ambiguously. It was just written very poorly.

Will the teacher admit that? Or is the expectation that this (likely neuro divergent) student should have just understood the expectations based on context clues or something?

I suspect many commenters are missing the point, the student's response can only be the correct and expected answer to this question. Teacher has it wrong.