The largest number that divides evenly into all numbers in a group of two or more numbers. To determine the greatest common factor of two numbers—for example, 12 and 16—list all the whole number factors of 12 (1, 2, 3, 4, 6, 12) and all the whole number factors of 16 (1, 2, 4, 8, 16). The greatest whole number that appears on both lists is 4, so 4 is the greatest common factor of 12 and 16. The smallest whole number multiple shared by all numbers in a group of two or more numbers. To nd the least common multiple of two numbers—for example, 5 and 6—list the rst few multiples of each number: 5, 10, 15, 20, 25, 30, and so on for 5, and 6, 12, 18, 24, 30, and so on for 6. The first (and, thus, least) multiple they share is the least common multiple (30). ;