GMAT Quantitative videos
The three videos below are explanations to the six most challenging math questions from the GMAT Review Official Guide 11th, 12th, and 13th Edition, Diagnostic Test. No need for any material - it is all re-printed in the video.
Note to SAT parents: GMAT math tests the same subjects as the SAT, just at a higher level. One difference is Geometry (as you will see). While the directions of each test indicate that geometric figures in GMAT Problem Solving and SAT I Math are drawn to scale (so figures can be eyeballed), every SAT figure will have an attached note that reads "NOTE: figure not drawn to scale". For the GMAT, such notes are typically not attached.