Double Number Line Diagrams

6.RP.3. Use ratio and rate reasoning to solve real-world and mathematical problems, e.g., by reasoning about tables of equivalent ratios, tape diagrams, double number line diagrams, or equations.

UPDATE (see below)

I just created a 9-minute video on the basic idea of double number line diagrams. Although double number line diagrams are specifically mentioned in a Grade 6 standard, if we want students to use them to solve ratio and rate problems in Grade 6, they really need to be familiar with the representations by then. That means they should be really introduced in elementary schools.

Anyway, I hope to create additional videos to elaborate how double number lines may be used to represent students' own reasoning, and eventually become their own thinking tools.

UPDATE: February 4, 2012
I just uploaded another video on double number line. I apologize for some background noises. Also, at one point I said something like "to go from 0.8 to 0.1..." when I really should have said "to go from 0.8 to 1..." The app I'm using does not allow me to edit the video, and I didn't want to re-do the whole video. So, please excuse my errors.