One third of pi multipled by the square of the radius Radius is 4,squared is 16 Multiply by pi is 50.26 One third of that is final answer 16.75 Best I can do.
@helenS I did briefly think it was a quarter because it's easier to work out,the radius squared and the quarter cancelling each other out but changed my thinking to a third of a circle.
Just a guess, I really didn't calculate, but I think the middle circle is divided into three equal parts. If its radius is given by [i]r[/i], then the green area should be π*r*r/3 Or maybe not? 😐
