Q20 of 79 Page 229

The inner curved surface area of a hemispherical dome of a building needs to be painted. If the circumference of the base is 17.6 m, find the cost of painting it at the rate of Rs 5 per sq. m.

Given : Circumference of base of dome = 17.6 m

Rate of painting = Rs 5 per sq.m


To find : Total cost of painting inside the dome = ?


Formula : Circumference = 2r


CSA of hemisphere = 2r2


Solution : Circumference of the base = 2r


⇒ 2 × × r = 17.6


r = = 2.8 m


The area to be painted = CSA of hemisphere = 2r2 = 2 × × 2.8 × 2.8 = 49.28 m2


Rate of painting = Rs 5 per sq.m


The total cost of painting = 49.28 × 5 = Rs 246.40


∴ The cost of painting the hemispherical dome on the inside is Rs 246.40.


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