Why This Student's Answer to Pizza Math Problem is Frustrating Everyone

A math problem posted to Reddit under the headline, "The American Education System is causing quite the debate. The question reads, 'Marty ate 4/6 of his pizza and Luis ate 5/6 of his pizza. Marty ate more pizza than Luis. How is that possible?' The student answered that Marty's pizza is bigger than Luis's pizza. The teacher, however, wrote that was wrong because 5/6th is greater than 4/6 so Luis ate more.