Operation sequence of four operations
1, addition, subtraction, multiplication and division are called four operations.
2. In the formula without brackets, if there is only addition, subtraction or multiplication and division, it should be calculated from left to right.
3. If there are multiplication and division and addition and subtraction in the formula without brackets, calculate the multiplication and division first and then the addition and subtraction.
4. If there are brackets in the formula, count the inner side of brackets first, and then the outer side of brackets; The calculation order of large, medium and small brackets is small → medium → large. The calculation order in brackets follows the above calculation order of 1, 2 and 3.
Four operating rules
1, additive commutative law: In the addition operation of two numbers, the positions of two addends are interchanged and the sum is unchanged. Letters indicate:
a+b=b+a
2, the law of addition and association: three numbers are added, first add the first two numbers, and then add another addend; Or add the last two numbers first, then add another addend, and the sum remains the same. Letters indicate:
(a+b)+c=a+(b+c)
3. Law of Multiplication and Interchange: In the multiplication operation of multiplying two numbers, the positions of the two multipliers are interchanged and the product remains unchanged. Letters indicate:
a×b=b×a
4. Multiplication and association law: When three numbers are multiplied, the first two numbers are multiplied first, or the last two numbers are multiplied first, and the product remains unchanged. Letters indicate:
(a×b)×c=a×(b×c)
5. Multiplication and distribution law: when two numbers are added (or subtracted) and then multiplied by another number, it is equivalent to multiplying this number by two addends (subtractions) respectively, and then adding (subtracting) the two products to keep this number unchanged.