The story of the professor and the policeman is very simple and ordinary, because I don't know how to write copy. This article is a series of articles, but the time of the previous and subsequent articles is not published in order, so that's gone.
Intention:
Reader comments
The meaning of the before and after crutches is different, which may be misleading to children. 4 Loses crutch 1, 4-1=3, but 0 gains crutch 1 and becomes 9 again. This is visualization rather than digitization. Children may think that 0+1=9. It wouldn't be a problem if an adult helps to understand.
The meaning of the before and after crutches is different, which may be misleading to children. 4 Loses crutch 1, 4-1=3, but 0 gains crutch 1 and becomes 9 again. This is visualization rather than digitization. Children may think that 0+1=9. It wouldn't be a problem if an adult helps to understand.