Addition operation is divided into: addition subtraction and addition combination. Multiplication operations are divided into: multiplication exchange method, multiplication combination method and multiplication distribution method. Division attribute: quotient invariant subtraction attribute: difference invariant decimal attribute. The law of additive exchange two addends exchange positions, unchanged. This is the law of addition exchange.

Alphabetic formula: a B=B a Example (simple calculation process): 6 18= 18 6=24 Additive combination rule: add the first two numbers or add the last two numbers first, which is called additive combination rule. Alphabetic formula: a B C=a(B C) Example (simple calculation process): 6182 = 6 (182) = 6 20 = 26.

Multiplicative exchange law: the concept of multiplicative exchange law is: two factors exchange positions and the product remains unchanged. Alphabetic formula: a×B=B×a Example (simple calculation process): 12×8=8× 12=96 Multiplication and division method: the concept of multiplication and division method is: the first two numbers are multiplied, or the last two numbers are multiplied first, and the product remains unchanged.

Alphabetic formula: a×B×C=a×(B×C) Example: 30× 25× 4 = 30× (25× 4) = 30×100 = 3000 Multiplication and distribution law: The concept of multiplication and distribution law is: the sum of two numbers, multiplied by a number, can be divisible. Alphabetic formula: (a, b)×C=a×C, b×C Example: (2,3 )×10 = 3×10, 2×10 = 30,20 = 50.

There is no simple two-digit operation formula, so there is a principle, that is, rounding method, rounding method for finding ten digits and hundred digits.