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
• B. 114
• C. 186
• D. 36

Answer 1

The correct option is A

150

Here, it is necessary to realise that the total surface area of an object is the total area of surface of an object that is visible to human eye. In case of a hollow cube, the internal surface is hidden and is completely invisible to us.
This means that for hollow cubes, surface area is just simply the external surface area. This is nothing but the sum of the areas of each face of cube (which is nothing but the total surface area of the cube).
We know that if ‘a’ is the edge of cube, area of one face is $a^2$.
Then the sum of areas of 6 faces will be $6a^2$.
Therefore, surface area of cube
$=6\times 5^2=150{\text{cm}}^2$