You don't. You use the GCF to reduce the answer once the addition or subtraction is complete.
The greatest common factor is used to reduce fractions.
To reduce fractions
One common application of greatest common factors is to simplify fractions. Note that you don't necessarily need the GREATEST common factor; you can simplify by dividing both numbers by any common factor, and then continue looking for additional factors.
When doing fractions it is the greatest common factor (GCF) and the least common multiple (LCM). You want the GCF when you are reducing fractions to their simplest form. When changing the denominators to a common one, you want the LCM.
Least common multiple is needed to find the least common denominator when adding or subtracting fractions with different denominators Greatest common factor is needed when reducing fractions to their lowest terms
Addition or subtraction of fractions require "like" fractions: that is, fractions with the same denominator.
In what type of problem exactly? For addition and subtraction of fractions
No. Common denominators are needed for addition and subtraction, not multiplication or division.
Yes. You need common denominators if you want to:Add fractionsSubtract fractionsCompare fractions ("which is larger?")You do not need common denominators to multiply or divide fractions. Thus, in the case of fractions, multiplication and division is actually easier than addition and subtraction.
Adding and subtracting fractions.Problems involving the addition or subtraction of unlike fractions
Knowing the least common multiple of the denominators will help you find a common denominator when adding and subtracting unlike fractions. Knowing the greatest common factor of the numerator and the denominator will help you reduce the fraction if possible.
those two operations are addition and subtraction.
It is usually called the least common multiple. But it can also be called the least/lowest common denominator when it is used for addition or subtraction of rational fractions.
Having a common denominator makes it easier to add or subtract fractions. You can also convert fractions to decimals and then do the addition or subtraction but that is really the same thing as having a common denominator of 10. 100. 1000. etc. Without a common denominator, you would have to mentally make adjustments for the values of fractions. Of course, that is really establishing a common denominator in your head.
If you apply it to the denominators, you could call it the least common denominator.
you have to compare the common fractions
In order to add and subtract fractions with unlike denominators, it is necessary to convert them to equivalent fractions with a common denominator. Example: 1/4 + 1/6 The LCM of 4 and 6 is 12. 1/4 = 3/12 1/6 = 2/12