The next part will start to get into the A/B level skill for this unit. We need to make sure you know what "greatest common factor" means. The greatest common factor (referred to as GCF after this) is the largest number that two numbers can be divided by to get a whole number. For example, the GCF of 8 and 10 is 2.
Sometimes, the greatest common factor is one of the numbers. For example, the GCF of 3 and 9 is 3. And sometimes, the only number both numbers can be divided by is 1.