1. The problem statement, all variables and given/known data Given a homogenous rectangular surface, sides of length a and b=4*a, with a circular hole in x=a and y=a/2, find the center of mass. 2. Relevant equations R=1/M*Ʃmi*ri , M= total mass, r= position vector area of a circle = pi*r2 , r being the radius 3. The attempt at a solution I determined the center of mass of the surface and circle and tried to subtract one from another, however the result did not agree with the solutions. Acircle=pi*r2 = pi*a2/4 Arectangle= a*4a = 4a2 Center of mass of the rectangle alone: Rr=(2a,a/2) Center of mass of the circle alone: Rc=(a,a/2) R=[Rr*Arectangle - Rc*Acircle] / Total area ⇔ ⇔R=a*(32-pi)/(16+pi) The correct center of mass is (2,05,a/2) Thanks! D.