Well, honey, the greatest common factor of 120 and 210 is 30. It's like finding the perfect pair of shoes that both numbers can comfortably slip into without any squishing or pinching. So, there you have it, 30 is the magic number that these two can both agree on.
The greatest common factor of 170 and 210 is 10
The greatest common factor of 105, 126, and 210 is 21
The GCF of 210, 252, and 294 is 42
210
The greatest common factor of 2940 and 3150 is 210. Source: http://www.mathwarehouse.com/arithmetic/numbers/GCF/greatest-common-factor-calculator.php