What I did:
r, radius of circle
d, diameter of circle
NOTE: diameter is also diagonal of square, therefore base of a triangle that is half of the square...
If you split the square into 2 triangles, they each have a height of r and a base of 2r...so...
Atri = 1/2(r)(2r) = r2
Asquare = 2(r2) = 2r2
We know the area of the circle must be 3.14r2
Now...to find the area of the circle outside the square we do: 3.14r2 - 2r2 = 1.14r2
To find the percent of the original circle that is, I think we do: 1.14r2
That rounds to about 36.3%, or 36% I guess...I think this should work...she explained the triangles thing...