The area of central circle would be : pi. d^2 /4
the area of the next region would be : pi ( d^2 - d^2/4) = 3/4 pi d^2
The outermost region would be : pi (9d^2 / 4 - d^2/4) = 5/4 pi d^2
Just multiply all equation with 4, you will get that the ratio will become 1 : 3 : 5
Hope this helps
