Question:
The slant height and base diameter of a conical tomb are $25 \mathrm{~m}$ and $14 \mathrm{~m}$ respectively. Find the cost of white washing its curved surface area at the rate of Rs 210 per $100 \mathrm{~m}^{2}$.
Solution:
It is given that
Slant height of conical tomb (l) = 25 m
Base radius (r) of tomb = 14/2 = 7m
Curved surface area of conical length tomb = πrl
= 22/7 ∗ 7 ∗ 25
$=550 \mathrm{~m}^{2}$
Cost of white washing $100 \mathrm{~m}^{2}$ area $=$ Rs 210
Cost of white washing $550 \mathrm{~m}^{2}$ area $=\operatorname{Rs}\left(\frac{210 * 550}{100}\right)=\operatorname{Rs} 1155$
Therefore the cost of white washing the whole tomb is Rs 1155.