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 at the rate of Rs. 210 per $ 100 \mathrm{~m}^{2} $.

AcademicMathematicsNCERTClass 9

Given:

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

To do:

We have to find the cost of white-washing its curved surface at the rate of $Rs.\ 210$ per $100\ m^2$.

Solution:

Slant height of the cone $(l) = 25\ m$

Diameter of the base $=14\ m$

This implies,

Radius of the base $(r)=\frac{14}{2}$

$=7 \mathrm{~m}$

Therefore,

The curved surface area of the cone $=\pi r l$

$=\frac{22}{7} \times 7 \times 25$

$=550 \mathrm{~m}^{2}$

Rate of white-washing $= Rs.\ 210$ per $100 \mathrm{~m}^{2}$

The total cost of white-washing the curved surface area $=Rs.\ \frac{550 \times 210}{100}$

$= Rs.\ 1155$

The total cost of white-washing the curved surface area is $Rs.\ 1155$.

raja
Updated on 10-Oct-2022 13:46:36

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