Addition, subtraction, multiplication and division are called four operations.
Among them, addition and subtraction are called first-order operations, and multiplication and division are called second-order operations.
operation sequence
When there is only one level of operation, it is calculated from left to right;
When there are two levels of operation, multiply first and then divide, then add and subtract;
When there is a layer of brackets, count the brackets first;
When there are multiple parentheses, count the parentheses first.
If there is a square, count it first.