The Bun

The three circles represent three buns, and it is simply required to show how these may be equally divided among four boys
The buns must be regarded as of equal thickness throughout and of equal thickness to each other. 
Of course, they must be cut into as few pieces as possible. 

To simplify it I will state the rather surprising fact that only five pieces are necessary, from which it will be seen that one boy gets his share in two pieces and the other three receive theirs in a single piece. 
I am aware that this statement "gives away" the puzzle, but it should not destroy its interest to those who like to discover the "reason why."

Math Genius