1, in the formula without brackets, if there is only addition, subtraction or multiplication and division, it should be calculated from left to right.

2. There are addition, subtraction, multiplication and division in the formula without brackets, so multiply and divide first, then add and subtract.

3. If there are brackets in the formula, calculate the inner side of brackets first, and then calculate the outer side of brackets; The calculation order of the formulas in brackets follows the above calculation order.