The calculation of addition can be done by exchanging two addends and checking them, or by subtraction. For example, 2 15+ 164=379 can be used for checking calculation. Similarly, he can also use subtraction to check and subtract an addend, which is equal to another addend. According to this method, we can list the following two formulas, or we can use 379-2 15= 164 or 379- 164=2 15.

The calculation of subtraction can exchange the positions of difference and subtraction, that is, the difference MINUS subtraction to see if it is equal to subtraction, so as to calculate. For example, 379-2 15= 164 can be calculated during inspection. You can also add the difference and subtraction to see if it is equal to the dividend, that is, add it to test. For example, 379-2 15= 164 can be calculated when checking, and 2 15+ 164=379.

In addition, pay attention to the vertical number, not necessarily the horizontal number. The number of checking computations is only to prove that the previous formula is correct.