When the numerator and denominator of a fraction are divided by a common factor at the same time, the value of the fraction remains unchanged. This process is called reduction. The basis for reduction is: the basic properties of fractions.

For example, a/b is a fraction. a can be written as c*d, b can be written as c*e, then a/b can be written as d/e, because there is a common factor c that can be canceled out for both the numerator and the denominator.

Simplest fraction: A fraction whose numerator and denominator have no common factors except 1 is called the simplest fraction.

Note: When reducing fractions, try to do mental arithmetic. Reducing a fraction to an equal fraction with a smaller numerator and denominator is called reducing the fraction. When reducing a fraction, use the common factor of the numerator and denominator (except 1) to divide the numerator and denominator of the fraction; usually, divide until the simplest fraction is obtained.

When reducing fractions, if you can quickly see the greatest common factor of the numerator and denominator, it is easier to directly use their greatest common factor to divide.