Nah, the kid’s right. Suppose Marty eats 4/6 of his pizza p1, and Luis eats 5/6 of his pizza p2, it means that for 4/6 p1 > 5/6 p2, p1 > (5/6)/(4/6) p2, which equals p1 > 5/4 p2

In other words, Marty’s pizza needs to be at least 25% larger than Luis’.