August 27, 2012 by Rogan Tinsley Leave a comment Sweet. The rule for 7 wasn’t around when I was a kid. themathkid: Try proving the rules for 7 and 11. It’s fun! Share this:TwitterFacebookEmailLike this:Like Loading... Related Author: Rogan Tinsley Biology, science and maths teacher with a PhD in Neuroscience and passion for education.