GCF and LCM. The biggest number that can evenly divide both. When we are trying to reduce a fraction. What is the greatest common factor (GCF) of two numbers ? When is the GCF useful?. D ivide the numerator and the denominator by their GCF. What is the simplest form of ?.
When finding a new common denominator for fractions so they may be compared, added, or subtracted.