what duz it mean to say "(a+b) is composite"?

Question

kirbykirby · Answer

It just means it is not prime, meaning there is a divisor that is not just 1 and itself

kirbykirby · Answer

For example, 2, 3, 5, 7, 11 are prime but 4, 6, 15, 21 are composite (2*2=4, 2*3=6, 3*5=15, 7*3=21)

anonymous · Answer

thanks! u r d best!

kirbykirby · Answer

:) np

anonymous · Answer

one mor fn...if u hv X={1,2,3,...,10} n aRb( a relates b) such dat (a+b) is composite. wat r the elements of the relation?

anonymous · Answer

is it (1,3),(1,5),(1,7),(1,8),...?

anonymous · Answer

@kirbykirby?

kirbykirby · Answer

yes it would be any pair (a,b) such that adding both together "a+b" gives a composite number 
Although I'm not too sure if the sum can't be greater than 10. I never saw this "Rb" notation. Does it say anywhere that (a+b) belongs to X ?

anonymous · Answer

i think so cuz it says "... and R a relation on X defined by aRb:a+b is composite"

anonymous · Answer

cuz X is limited on d range 1-10

anonymous · Answer

wat do u fnk?

kirbykirby · Answer

ok then I would think that the sum can't exceed 10 (but I am not 100% sure o_o)

anonymous · Answer

me neither. thanks anyway

kirbykirby · Answer

but fairly certain. Otherwise I think you'd have too many pairs to list lol