Extracting common factors is a mathematical method that has appeared since the third and fourth grades of primary schools, and it is also needed in the fifth and sixth grades; The method is to put two or more factors with the same number outside brackets, which is also called the reverse application of multiplication and division.

Extracting common factors is widely used in the process of multiplication, which may be integers in grade three or four, or integers, fractions or decimals after senior grades.