A closed metallic cylindrical box is 1.25 m high and its base radius is 35 cm. If the sheet metal costs Rs. 80 per m², the cost of the material used in the box is :

Solution(By Examveda Team)

Total surface area :
$$\eqalign{ & = 2\pi r\left( {h + r} \right) \cr & = \left[ {2 \times \frac{{22}}{7} \times \frac{{35}}{{100}} \times \left( {1.25 + 0.35} \right)} \right]{{\text{m}}^2} \cr & = \left( {2 \times \frac{{22}}{7} \times \frac{{35}}{{100}} \times \frac{{16}}{{10}}} \right){{\text{m}}^2} \cr & = 3.52\,{{\text{m}}^2} \cr} $$
∴ Cost of the material :
$$\eqalign{ & = {\text{Rs}}{\text{.}}\left( {3.52 \times 80} \right) \cr & = {\text{Rs}}{\text{. 281}}{\text{.60}} \cr} $$