What is 2 3rds of a circle?

Answer 1

It depends on the shape that is removed.

It could be a smaller circle, whose radius is sqrt(2/3) = 0.8165 of the original radius,

Or a circle with a hole with radius sqrt(1/3) = 0.5774 of the original radius cut out of it,

Or a wedge making a central angle of 120 degrees removed from the circle,

Or more complicated shapes.