The older I get, the more I appreciate the ones who have helped me along the way. One of the first memories I have about math came in 1st grade when my father showed me a trick about subtraction; in fact, I teach my students this technique when I notice there a delay in his/her basic subtraction. Thanks, Dad for the lesson! Here is a video I made years ago that isn’t graphing-based, but I feel compelled to share. Enjoy!