1. Swap two addend positions and recalculate.

2. Subtracting one addend equals another addend.

"Checking calculation" is a mathematical term, which means that after the problem is calculated, it is calculated by inverse operation to check whether the result of the previous operation is correct.

For example, subtraction is used to solve problems, addition is used to solve problems, subtraction is used to solve problems, multiplication is used to solve problems and division is used to solve problems. Checking calculation can effectively find errors in the calculation process, but it is not very useful for solving problems. Compare the data obtained by checking calculation (using the results to derive conditions) with the original data, and prompt whether the operation is correct.