A common factor is a factor that two or more numbers have in common or share.
Example #1
The factors of 6 are 1, 2, 3, and 6
The factors of 4 are 1, 2, and 4
A common factor of 4 and 6 is 2.
However, notice that 1 is also a common factor.
Example #2
The factors of 6 are 1, 2, 3, and 6
The factors of 4 are 1, 2, and 4
The factors of 15 are 1, 3, 5, and 15
The only common factor of 4, 6, and 15 is 1.
1 is always a common factor of two or more numbers because any number is divisible by 1.
The common factor is also called common divisor.