What is the greatest common divisor of positive integers m and n?
1) m is a prime number
m is prime. n can be any thing but their GCD will always be 1. The only common divisor of a prime number and any other number is 1. How ever if m=n GCD=m=n. Hence insufficient
2) 2n = 7m
n= 7m/2 means m is divisible by 2. so m can be 2, n can be 7 with GCD 1 or m =4 and n =14 and GCD =2. Hence Insufficient
Together, m is prime and 2n=7m implies means m=2. M is the only even prime. m=2 and n=7