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CBSE Class 9 Mathematics Question 6 of 44

Surface Areas and Volumes — Question 6

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Question

Question 6

The slant height and base diameter of a conical tomb are 25 m and 14 m respectively. Find the cost of white-washing its curved surface at the rate of ₹ 210 per 100 m2.

Answer

Given,

Diameter of conical tomb (d) = 14 m

Radius of conical tomb (r) = Diameter2=142\dfrac{\text{Diameter}}{2} = \dfrac{14}{2} m = 7 m.

Slant height of conical tomb (l) = 25 m

The slant height and base diameter of a conical tomb are 25 m and 14 m respectively. Find the cost of white-washing its curved surface at the rate of ₹ 210 per 100 m^2. NCERT Class 9 Mathematics CBSE Solutions.

By formula,

Curved surface area of conical tomb = πrl

= 227\dfrac{22}{7} × 7 × 25

= 550 m2.

Given,

Cost of white-washing 100 m2 area = ₹ 210

Cost of white-washing 550 m2 area = ₹ 210×550100210 \times \dfrac{550}{100} = ₹ 1155.

Hence, the cost of white-washing the conical tomb is ₹ 1155.