Question

a closed cubical box of edge 20cm is made up of wood of thickness 2cm. find the: a)volume of wood b)volume of air trapped in it

Answer 1

Size of the edge (external) of the cube = 20 cm
Width/thickness of the wood :  2 cm

Along each edge there are two planks/plates/surfaces of wood. So the size of the edge of inner cube (inside) that contains air =  20 - 2 * 2cm = 16 cm

Volume of air contained inside = 16³ cm³ = 4, 096 cm³
External volume of the cube = 20³ = 8,000 cm³

The volume of wood used = 8000 - 4,096 = 3, 904 cm³