# Ex.13.3 Q6 Surface Areas and Volumes Solution - NCERT Maths Class 9

## Question

The slant height and base diameter of a conical tomb are $$25\rm\, m$$ and $$14\rm\, m$$ respectively. Find the cost of white washing its curved surface at the rate of $$\rm\,Rs \,210$$ per $$100$$ $$\rm\,{m^2}$$.

Video Solution
Surface-Areas-And-Volumes
Ex exercise-13-3 | Question 6

## Text Solution

Reasoning:

Curved surface area of a right circular cone of $$r$$ base radius and slant height is $$\pi rl$$.

What is known?

Slant height and base diameter rate of white washing $$\rm Rs\, 210$$ per $$100$$\begin{align}\rm\,{m^2} \end{align}.

What is unknown?

Cost of white washing its curved surface area.

Steps:

Slant Height $$(l) = 25\rm\, m$$

\begin{align}r = \frac{{14}}{2} = 7\rm\,m \end{align}

Curved surface area \begin{align} = \pi rl \end{align}

\begin{align} &= \frac{{22}}{7} \times 7 \times 25\\&=550\rm\,\,{m^2} \end{align}

Cost of white washing per \begin{align}100\rm\,\,{m^2} \end{align} $$= 210$$

\begin{align}{\rm{For}}\,\,550\rm\,\,{m^2} &= \frac{{210 \times 550}}{{100}}\\ &= {\rm{ Rs }}\,1155 \end{align}

Answer:

Cost of white washing the conical tomb is $$\rm Rs.\, 1155.$$

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