Common Factors:A Common Factor of a set of numbers is a factor of each of the original numbers - or in other words, it is contained as a factor in each of the original numbers.Just as with common multiples, it is easy to see if something is a common factor by looking at its prime factors.Example 1: 18 is a common factor of 90 and 36 18 has prime factors 2*3*3 90 has prime factors (2*3*3)*5, and s