Four operations are simple and basic mathematical operations, that is, four operations of addition, subtraction, multiplication and division. Four operations are the important content of primary school mathematics and the basis of learning other related knowledge.

Four operations are an important part of the development of mathematics. Their origin can be traced back to the development of ancient civilization. After continuous exploration and improvement by mathematicians, it has become the most basic and commonly used operation method in modern mathematics.

Nature of operation:

Properties of 1. addition operation

From additive commutative law's associative law, it can be concluded that when several addends are added, the positions of addends can be exchanged at will; Or add a few addends first and then add them with other addends, and the sum remains the same. For example: 34+72+66+28 = (34+66)+(72+28) = 200.

2. The essence of subtraction operation

Subtracting the sum of two numbers from a number is equivalent to subtracting each addend in the sum from this number in turn. For example:134-(34+63) =134-34-63 = 37.

A number minus the difference between two numbers is equal to this number minus the minuend in the difference, and then the subtraction. For example: 100-(32-15) =100-32+15 = 68+15 = 83.

If you subtract a number from the sum of several numbers, you can choose any addend to subtract this number and add it to the rest of the addends. For example: (35+17+29)-25 = 35-25+17+29 = 56.

If you subtract several numbers from a number in succession, you can add all the subtractions first, and then subtract the sum of the subtractions from the minuend. For example: 276-115-85 = 276-(115+85) = 76.

3. The essence of multiplication

Multiply the product of several numbers by a number so that any factor in the product can be multiplied by this number and then multiplied by other numbers. For example: (25×3 ×9)×4=25×4×3×9=2700.

Multiply a number by the difference between two numbers, and you can multiply the minuend and the minuend by this number respectively, and then subtract the product. For example: (137-125) × 8 =137× 8-125× 8 = 96.