1. Addition and subtraction formula: add the first addend to the whole ten, whole hundred and whole thousand of the second addend, and then subtract the difference between the second addend and the whole ten, whole hundred and whole thousand, which is equal to the sum.

2. Finger formula

The index finger extends "L" and the middle finger extends "2".

The ring finger is "3" and the little finger is "4".

Four fingers and a thumb, the thumb is "5" to remember;

Then extend the index finger to the little finger, and "6", "7", "8" and "9" are arranged in numbers.

3. Find the sum of only two digits in the position transformation of two digits.

Mouth formula: (beginning and end) × 1 1= and children's addition and subtraction finger quick calculation.

4. Practice the formula with your left finger.

Ten, twenty, thirty, forty; Fifty,

Sixty, seventy, eighty, ninety, one hundred.

5. One-eye three-line addition formula

Forward 1, discard 9 in the middle, and finally discard 10. Children's addition and subtraction finger quick calculation.