how do i find the GCF with addition for example 15+21 ?
i feel so slow right now

Question

anonymous · Answer

@ganeshie8 @Nnesha @Aliypop

phi · Answer

it helps to know 1) prime numbers. I would memorize the first few on this list https://en.wikipedia.org/wiki/List_of_prime_numbers#The_first_500_prime_numbers 2,3,5,7,11,13 2) the "divisibility rules" https://en.wikipedia.org/wiki/Divisibility_rule#Divisibility_rules_for_numbers_1.E2.80.9320 learn the rules for 2,3,4,5,6 and 9

phi · Answer

if you learn that stuff, then you will be able to write your problem
15+21
as
3*5+3*7
now you can see the biggest number in both terms is 3
so 3 is the GCF

anonymous · Answer

ok thx i just refreash on it