The slant height and base diameter of a conical tomb are 25 m and 14 m respectively.
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.