Off-form calculation, also known as recursive calculation (the name of recursive calculation is used in mathematics of Shanghai Education Edition of Grade Three), needs to write down the calculation process completely, which is divorced from vertical calculation.

Out-of-type calculation calculates one formula at a time until the final result is calculated.

Operation sequence of four operations:

In the formula with brackets, the inside of brackets should be counted first, then the inside of brackets, and finally the outside of brackets.

1, elementary arithmetic order: in the same level of operation, it is calculated from left to right in turn; In the two-stage operation, multiplication and division are performed first, and then addition and subtraction are performed.

When there are brackets, count the inside of the brackets first, and then the outside of the brackets. When there are multiple brackets, first calculate the inside of brackets, then calculate the inside of braces, and finally calculate the outside of brackets.

2. Multiplication is a simple operation of addition, division is a simple operation of subtraction, subtraction and addition are reciprocal operations, and division and multiplication are reciprocal operations.

When several addends are added, the positions of addends can be exchanged at will, or several addends are added first and then added with other addends, and the sum remains unchanged.

Subtracting the sum of two numbers from a number is equivalent to subtracting each addend in the sum from this number in turn.