Question

A cube whose edge is 20 cm long has circle 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 area possible?

Answer 1

If its a cube then all of its sides are of same length that is 20 cm

and the circle will have 20 cm as its diameter

surface area of a cube = 6a^2 = 6(20)^2 = 2400 cmsq will be the surface area of cube

there will be a circle on each of the 6 faces so the area of the circles will be

6 * Pi.r.r ( where Pi = 3.14 and r is the radius)

6*3.14*10*10 = 1884 cmsq

Area of the unpainted surface = 2400 - 1884 = 516 cmsq