The gcf of any two odd numbers is always odd

True, greatest common factor of 2 odd numbers will always end up as odd numbers.
What is GCF by the way, GCF or also known as greatest common factor is the 2 numbers largest factor that they have in common.
 In order to check if 2 odd numbers’ GCF will always be odd number, is to try to choose any to odd numbers, then write down all the factors they have. Next look for the greatest factor they have in common and check if it’s an odd number.

38+105= 143, 39+104=143, and you will find then adding the numbers on opposite sides, moving inwards yields the answer 138 every time. because of this, you’re going to multiply 138 times the number of pairs, which is 34. therefore, 34*138= 4692(i’m sorry if it’s the wrong numbers, but it’s the right concept)