Book 4 teaches rhythms: 2 notes on 1 count, held over notes, quick notes and triplets. Students learn to play an additional 30 songs using these fun rhythms. CDs in two formats accompany Books 1-4 to assist learning through listening, format 1 is classic piano, format 2 is 'crazy combo'- different for every song. For more information visit www.MaryWrightBooks.com