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."