This is the first video in the GRE Math review series.The topic is Basic Arithmetic concepts. I follow the 19th Ediition Barron's GRE book. This is the first topic in the Math Review Section (11-A, page 228-244). After you view the video, try the practice questions on Pg 245-247.
If you have any questions, feel free to write it in comments below. Good luck!