In this video I show that the "vortex sum" of a number (summing up the digits until obtaining a single digit is obtained) is just the remainder when dividing the number by 9. I go over a couple of examples while also illustrating why this is the case by writing the transition numbers 10, 100 as (9 + 1), (99 + 1). YouTube - Summary - Notes - Playlist
#math #vortexmath #modulararithmetic #algebra #education