Caculate if a value is greater or less than some % of the next value

Let's assume I have a vector a=[1,2,3] b=[0.5,3,8] is there an if statement that can check if a(i) is greater or lower in the same time than b(i) in 5% . rather than check 5% up and 5% down. what is the code that will do it? thanks.

something like if(a(i)=abs(5% of b(i))) do so and so else break;