If gcd(a,100)=5\gcd(a, 100) = 5gcd(a,100)=5 and gcd(b,100)=10\gcd(b, 100) = 10gcd(b,100)=10, what is gcd(a+b,100)\gcd(a+b, 100)gcd(a+b,100)?
5
10
15
20