Simple operation has always been a difficult problem in primary school mathematics. Many students can recite the operation theorem by heart, but in the process of solving problems, they often have no way to start. The following are some simple calculation formulas that my students and I summarized in the actual problem-solving process, hoping to bring some new enlightenment to everyone.

1. In the operation at the same level, the positions of numbers can be exchanged at will, but they should be exchanged with the previous symbols. (addition or multiplication commutative law)

2. In the operation at the same level, brackets can be added and removed directly after the plus sign or multiplication sign. Add brackets after minus sign and division sign, delete brackets, and change the symbols in brackets. (law of addition or multiplication)

3. Make up one law, ten laws, a hundred laws and a thousand laws: "Make up nine before, make up ten after".

Be sure to remember: 25 replace 4 with 100, 125 replace 8 with 1000 (rounding idea).

4. Comprehensive formula (including various algorithms)

Simple operations round up integers, exchange them first and then combine them; A number MINUS several numbers in a row is equal to the sum of the subtracted numbers; A number divided by several numbers in succession is equal to the product of this number divided. Several numbers are multiplied and then added separately, and several numbers are multiplied and then subtracted separately. Give the same number and put the rest in brackets. More reduction, more increase, less increase, less decrease.

Example: