MATH 120 Ch10 Part D1 - Addition in Base 7 - YouTube
Number Bases (Addition and Subtraction) - YouTube
Amazon.com: BYJU'S Learning: Disney 1st Grade Premium Edition for iPhone & iPad (App+8 Workbooks) Ages 5-7, Featuring Disney & Pixar Characters-Reading, Addition/Subtraction, Writing&Phonics-Osmo Base Included : Toys & Games