On the whole, Only's mental arithmetic is not bad. I'm a mental arithmetic teacher, filling in for 10 years. I have taken care of nearly 2000 children. From the children I take care of, I can feel that the children are really changing, and the longer I study, the better the effect. I feel that I have done a good job of connecting young children and basically solved the problem that the calculation method is inconsistent with that of primary schools. Teaching methods are more interesting. I think if your child is between 4- 10 years old, you'd better sign up for study. Don't miss it!