1, increase and decrease difference method: add the preceding addend to the following integer, and subtract the difference between the following addend and the integer to get the sum.

2. Subtraction plus difference method: Subtracting the integer of subtree and adding the difference between subtree and integer equals the difference.

3. Difference between two complements: two complements are subtracted, and the minuend is subtracted by 50 times 2; Subtract three complements and be subtracted by 500 times 2; Four complements are subtracted, and the subtracted 5000 is multiplied by 2, and so on.

4. The sum of two digits is reversed: the ten digits of a number plus its single digits multiplied by 1 1 equals the sum.

Extended data:

Decimal method is: when the unit is not reduced enough, subtract the subtraction with 10 and add the remainder to the unit, that is, decimal method.

Break the ten-law formula

A dozen MINUS nine, a few plus one; Ten MINUS seven, a few plus three; A dozen MINUS five, a few plus five; One dozen MINUS three, several plus seven; A dozen MINUS eight, a few plus two; A dozen MINUS six, a few plus four; A dozen MINUS four, a few plus six; A dozen MINUS two, a few plus eight.