1, the bead is not enough, and the next 5 is reduced;

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.

Extended data:

Children's mental abacus calculation refers to the mental abacus calculation of preschool children aged 4-6 in class. The whole process of children's mental abacus calculation is: lightning counting-instant counting-calculating bead image-simulating bead pulling-internalizing bead image. This continuous action transforms abstract thinking into image thinking, and they are used alternately to promote the balanced development of children's left and right brains. Therefore, "abacus mental arithmetic" is better in developing intelligence. It is the golden key for children to develop their intelligence. "

Children's song formula

Add one, please dial double nine, we are all good friends;

Add two, please dial double eight, laugh when you are happy;

Add three, please dial double seven, sometimes you will be angry;

Add four, please dial double six, and jump if you are happy. If you subtract one, please dial double nine and sing like a lark;

If you subtract two, please dial double eight, don't delay too much;

If you subtract three, please dial double seven and queue up neatly to do exercises;

If you subtract four, please dial double six. Don't sleep late in the morning.

Baidu Encyclopedia: Children's abacus mental arithmetic