This is one of the early probability activity that I do with my students. They fill in the addition chart and find numbers that are more likely, less likely , and impossible when adding two numbers.
I am a third generation public school teacher who has been in education since 1987. I have taught elementary students full time for 20+ years. I am also a freelance curriculum writer. You can contact me at mrs.mjbauer(at)gmail(dot)com.