Let's assume we were given 2 numbers: 15 and 30. their sum is: we want to express it as the product of gcf and another sum.15 is divisible by: 1, 3, 5, 1530 is divisible by: 1, 2, 3, 5, 6, 10, 15, 30the greatest number that appears in 2 series is 15.in this case sum of two numbers can always be written as: