The question is all one digit plus one digit addition. No time limit. When I try it, it gets hot in the middle and I feel like doing it to the end of 100 questions. It's simple, but it's fun to try, and when you reach the goal, you'll get a strange exhilaration, a sense of accomplishment, and above all, a sense of self-affirmation. It can be enjoyed by everyone from elementary school students to the elderly.