A hemispherical dome is open from its base and is made of iron. Thickness of dome is 3.5 meter. Total cost of painting domes outer curved surface is Rs. 2464. If the rate of painting is Rs. 8 per meter2, then what is the volume (in meter3) of iron used in making dome?

A hemispherical dome is open from its base and is made of iron. Thickness of dome is 3.5 meter. Total cost of painting domes outer curved surface is Rs. 2464. If the rate of painting is Rs. 8 per meter2, then what is the volume (in meter3) of iron used in making dome? Correct Answer 628.83

Outer curved surface area = Cost of painting the surface / Rate of painting

⇒ 2464/8 = 308 m2

Outer curved surface area = 2πRo2

308 = 2 × 22/7 × Ro2

(308 × 7) / (2 × 22) = Ro2

49 = Ro2

Ro = 7 m

Ri = Ro - thickness = 7 - 3.5 = 3.5 m

Volume of the hemispherical dome = 2/3 π (Ro3 - Ri3)

⇒ 2/3 × 22/7 × (73 - 3.53) = 628.83 m3

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