One thing that puzzles a lot of young algebrists is the factors in a word problem that are taken as "understood". This presentation on solving systems of linear inequalities does a great job walking the learner through how to tease those...

How many times have you traveled around the sun? Aspiring astronomers grasp what a year is and they differentiate between orbit and rotation by walking around the sun right within your classroom. Place a lamp in the center of the room to...