Theory about fractions
31_UNIT 3: All about fraction
https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B_mLCq2y0KwvMDE5ODBiMWQtYzUyYi00NmQwLTgxODQtMjI0MDg5YzEzMTYz&hl=es
Exercises you have to do:
31_ UNIT 3: Exercises about fractions