Question

There is hollow cube. Its external edge is 5 cm long and its internal edge is 3 cm long. What is its surface area in $c{m}^2$ ?

• A. 150 $c{m}^2$
• B. 36 $c{m}^2$
• C. 186 $c{m}^2$
• D. 114 $c{m}^2$

Answer 1

The correct option is A

150 $c{m}^2$

It is necessary to realise that the Total surface area of an object is the total area of surface of object visible to the human eye. For a hollow cube, the internal surface is hidden and completely invisible to us.

This means that for hollow cubes, surface area is just simply external surface area.

This is nothing but the sum of the areas of each face of cube.

We know that if $‘a^{\prime }$ is the edge of cube, area of one face is $a^2$.

The sum of all face areas is 6$a^2$ because there are 6 faces.

$\therefore$ Area $=6\times 5^2=6\times 25=150c{m}^2$