2, the beads are not reduced enough, go to 5' s complement;

3, a file is not enough, plus 10 minus make up;

4. If the number of files is not enough, subtract 10 and add the complement to make up the number: the two numbers add up to 5; Complement: The sum of two numbers is equal to 10.

Mental arithmetic of magic ink beads is a method of turning numbers into abacus symbols by virtue of intuitive impression of abacus calculation, and calculating according to abacus calculation principle. Abacus mental arithmetic originated from abacus calculation, which describes the disk type, grade and abacus calculation in the brain and completes abacus calculation in the "heart" without using the physical abacus.

Extended data:

The heart is counted from the low position. The course of mental arithmetic contains a lot of knowledge of mathematical concepts, not just calculation. The concept of quick mental arithmetic is more important than calculation. The arrangement of mental arithmetic teaching method is made according to the age characteristics of children. Combining situational teaching with interesting teaching, children play in school and middle school.

Mental arithmetic teaching focuses on the experience of logarithm concept in children's life, and then teachers integrate the understanding of logarithm in children's life into teaching. Although it is called mental arithmetic, it contains all the concepts of numbers in the primary school mathematics curriculum. Therefore, quick heart is the best choice for children's mathematics curriculum.

Baidu encyclopedia-mental arithmetic