Analysis: In a formula that only contains operations at the same level, it is generally necessary to calculate from left to right.
If there are two levels of operation, multiply and divide first, and then add and subtract; If there are brackets, count them first.
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, 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. Primary to secondary operation. If an expression contains both 1 level operation and 2-level operation, the 2-level operation should be calculated first, and then the 1 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 operation order mentioned above, you need to use brackets. There are three kinds of brackets commonly used: parentheses, marked as (); Parentheses, marked []; 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.