Formula of mixed operation sequence of addition, subtraction, multiplication and division: parentheses are calculated first, multiplication and division are calculated first, and then addition and subtraction are calculated. If there are both braces and parentheses, count the parentheses first and then the braces.

The mixed operation of grades three and four is generally not so complicated, with brackets, addition, subtraction, multiplication and division. Usually, as long as there are parentheses, the parentheses are calculated first. Without parentheses, the operation method will definitely not go wrong.

Of course, there are also individual formulas. If there is a formula that needs simple operation, we should first observe the relationship between the multiplication of the formula and the equation.