It is suggested to contact the math teacher and ask the math teacher to recommend teaching AIDS according to the child's level. Since you have spent money, you can get the most benefit, right?

What I recommend is that the small champion is suitable for children of upper-middle level.

As for where to buy it, Xinhua Bookstore must have it. If you are not in a hurry, both Zhuoyue and Dangdang support cash on delivery.