A cube whose edge is 20 cm long, has circles on each of its faces painted black. What is the total area of the unpainted surface of the cube if the circles are of the largest possible areas?
Answer: D
Diameter of largest circle = 20 cm.
∴ Area of circle = 100π cm⊃2;
∴ Area of 6 circles = 6 × 100π = 600π cm⊃2; (∵ there are six faces in a cube)
Also, Area of cube = 6 × (20)⊃2; = 2400 cm⊃2;
Area of unpainted surface = 2400 – 600π
= 2400 – 600 × 22/7
= 514.28 cm⊃2;.