The dimensions of an open box are 52 cm × 40 cm × 29 cm. It thickness is 2 cm. If 1 cu.cm of metal used in the box weight 0.5 gm, then the weight of the box is :

Since the box is an open one, we have :
Internal length = (52 - 4) cm = 48 cm
Internal breadth = (40 - 4) cm = 36 cm
Internal depth = (29 - 2) cm = 27 cm
Volume of the metal used in the box :
= External volume - Internal volume
= [(52 × 40 × 29) - (48 × 36 × 27)] cm³
= (60320 - 46656) cm³
= 13664 cm³
∴ Weight of the box :
$$\eqalign{ & = \left( {\frac{{13664 \times 0.5}}{{1000}}} \right){\text{kg}} \cr & = 6.832\,{\text{kg}} \cr} $$