Count the brackets first, then the ones without brackets.

Addition and subtraction mixed arithmetic: addition, subtraction, multiplication and division, collectively referred to as four operations.

Among them, addition and subtraction are called first-order operations, and multiplication and division are called second-order operations.

1, when there is only one-level operation, it is calculated from left to right;

2. When there are two levels of operation, multiply first and then divide, and then add and subtract.

3. When there is a layer of brackets, count the brackets first;

4. When there are multiple brackets, count the brackets first.

5. If there is a square, count it first.

6. When mixing operations, count the parentheses first, from small to large. Then from high to low.

For example: 1, 59-(30+20)=59-50=9.

2、200+(400+30)=200+430=630

3、280-(80-60)=280-20=260?

4、35+500-200=535-200=335