A cube whose edge is 10 cm long, has circles on each of its faces painted red. What is the total area of the unpainted surface of the cube if the circles are of the largest possible areas? (Take \(\pi=3.14\))
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 129 cm2
The largest circle that fits on a square face touches all four sides, so its diameter equals the edge, 10 cm, and its radius is 5 cm. On each face, the unpainted part is the square minus the circle.
Area of one face \(=10\times10=100\) cm2
Area of one circle \(=3.14\times5\times5=78.5\) cm2
Unpainted part of one face \(=100-78.5=21.5\) cm2
Unpainted surface of the cube \(=6\times21.5=129\) cm2