The main thing to master is to remember to calculate multiplication and division first, and then add and subtract. In the successive calculation of multiplication and division, it should be calculated from left to right. When you encounter parentheses, you must first calculate the inside of parentheses. In the process of separation, the operation sequence line should be drawn according to the operation sequence, and the "three checks" should be done well. First of all, check whether the numbers and symbols copied from books to exercise books are correct. Second, check whether the numbers and symbols copied from horizontal to vertical are copied correctly. Third, it is necessary to check whether the draft is copied vertically, horizontally, and whether the decimal point position is correct or not.

Four operation sequences

Among the four operations, addition and subtraction are called primary operations, and multiplication and division are called secondary operations. Expressions that contain two or more operations are usually called mixed operations. The mixed operation of addition, subtraction, multiplication and division is also called elementary arithmetic. In elementary arithmetic, the prescribed calculation order is called operation order. Mathematically speaking, the order of these four operations is as follows:

(1) sibling operations In an expression, if only sibling operations are included, the operations should be performed from left to right. That is to say, only addition and subtraction, or only multiplication and division are mixed operations, and their operation order is calculated from left to right.

(2) One-to-two operation

In an expression, if both first-level operation and second-level operation are included, then the second-level operation should be calculated first, and then the first-level operation should be calculated. That is, "multiply first and then divide, then add and subtract", or "multiply first and then divide, then add and subtract" for short.

(3) Operation with brackets

If you want to change the order of the operations mentioned above, you need to use parentheses. There are three kinds of brackets commonly used: parentheses, marked as (); Parentheses, marked as [; Braces, marked {}. When using the bracket, pull on both sides and add in the middle. Use parentheses first, then brackets, and finally braces.

If there are several kinds of parentheses in an expression, the multiplication or division in parentheses should be calculated first, then the addition or subtraction in parentheses, and finally the parentheses. When calculating, you should first calculate the formulas in brackets in the order mentioned above, and then calculate the results in the order of the numbers outside brackets.