NCERT Class 9 Solutions: Surface Areas and Volumes (Chapter 13) Exercise 13.3 – Part 3
Q6 The slant height and base diameter of a conical tomb are and respectively. Find the cost of whitewashing its curved surface at the rate of per Solution:
We know,

Base diameter =

Radius (r)

Slant height of tomb (l)
Therefore curved surface area =
Rate of white washing 100 m^{2}
Rate of white washing 1 m^{2}
Therefore, total cost of whitewashing the tomb with area
Q7 A joker’s cap is in the form of a right circular cone of base radius and height . Find the area of the sheet required to make such caps.Solution:

The cone radius (r)

The cone height (h)
Now, l be the slant height
Sheet required for one cap = Curved surface of the cone
Sheet required for
Q8 A bus stop is barricaded from the remaining part of the road, by using hollow cones made of recycled cardboard. Each cone has a base diameter of and height 1 m. If the outer side of each of the cones is to be painted and the cost of painting is , what will be the cost of painting all these cones? (Use and take )
Solution:
We are given,

Radius of the cone (r)

Height of the cone (h)
Now, the slant height of a cone is given by
We know that, rate of painting
Curved surface area of 1 cone =
Therefore, curved surface of such 50 cones =
Finally, cost of painting all these cones is (since, the cost of painting is )