What the teacher taught me is right. This is the "ten-point method" in the first grade mathematics: it means to circle 10 first, and then add two outside the circle, which is 10+2= 12. The simplest way is: see 9 thoughts 1. Please read ten songs together: 19 19 years of good friends. Let's go together. Five plus five makes a pair of hands. When we see 9, we think of 1, 8, 2, 7, 3, 6, and we think of 4. When we see children with decimal system, we should remember that "9 Yao 1", "8 Yao 2", "7 Yao 3", "6 Yao 4" and "5 Yao 5" make up ten. The thinking process is simple and easy.