Small thing but hey if you hear someone working through simple math out loud, please don't tease them about it unless you truly know it's welcome.
Dyscalculia is like dyslexia with numbers, people who struggle with it frequently make simple math errors. These are often reduced if we say the numbers out loud. Cracks about whether someone can calculate a tip or do other everyday math in their head...it can feel very not funny, and increase anxiety (making the calculating harder).