If the length = 5w then length to width = 5/1. This also means we could create a rectangle B with width 1 and length 5 and have it be the same shape, if not size as the rectangle in the question(A).
The area of any rectangle is (l)(w) and the perimeter is (l+w)^2. so the ratio with our rectangle B would be (5)(1)/(5+1)^2. Simplifed, 5/12. This is also the simplifed ratio of rectangle A.