Arithmetic/More About Multiplication/The Greatest Common Factor
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The Greatest common Factor (GCF) of two whole numbers is the highest number that can be divided by both of the original numbers to get a whole number result.
Finding the GCF of a number 
- Write down to prime factorization of the two numbers.
- Find prime factors that are the same.
- Multiply the same prime factors together for the GCF.
- Notice that two and seven are used in both the equations?
Therefore, the GCF of 28 and 98 is 14.