A circular grassy plot of land, 42 cm is diameter, has a path 3.5 m wide running around it outside. The cost of gravelling the path at Rs. 4 per square metre is :

Radius of the plot = 21 m
Area of the path :
$$\eqalign{ & = \pi \left[ {{{\left( {24.5} \right)}^2} - {{\left( {21} \right)}^2}} \right]{m^2} \cr & = \left[ {\pi \left( {24.5 + 21} \right)\left( {24.5 - 21} \right)} \right]{m^2} \cr & = \left( {\frac{{22}}{7} \times 45.5 \times 3.5} \right){m^2} \cr & = 500.5\,{m^2} \cr} $$
∴ Cost of gravelling :
= Rs. (500.5 × 4)
= Rs. 2002