If a and b are positive integers, what is the value of a + b ?
(2) The greatest common divisor of a and b is 1
1) a/b =5/8
a=5 ; b=8; a/b =5/8 ; a+b =13
a=10 ;b=16 ;a/b =5/8 ;a+b=26
2) insuff ...no information about values of a and b .
Together sufficient: if GCD of a and b is 1 , only possible values of a and b are 5 and 8 respectively, so a+b=13