Comparing fractions: are the wholes the same size?

Sometimes we cannot compare two fractions, or if we do, we end up with strange situations. When is a comparison valid? It turns out, the wholes that the fractions refer to have to be the same size.
Find math videos for 3rd grade:
www.mathmammot...
Math Mammoth Grade 3 Curriculum:
www.mathmammot...
Online practice for ordering fractions on a number line:
www.mathmammot...