"Question 5 A hemispherical bowl made of brass has inner diameter 10.5 cm. Find the cost of tin-plating it on the inside at the rate of Rs 16 per 100 cm^2 .
Class 9 - Math - Surface Areas and Volumes Page 225"
Answers
radius of inner part = 21/4 cm
surface area of inner part of bowl = 2πr²
= 2 × 22/7 × (21/4)²
= 11/7 × 21/4 × 21
= 33×21/4 cm²
now, cost of painting inside the bowl = inner surface area of the bowl × rate
= 33×21/4 × 16/100
= 33×84/100 ₹
= 27.72 ₹
Hemisphere:
When a plane through the centre of a sphere divides the sphere into 2 equal parts then these two equal parts are called hemisphere.
Diameter:
A line segment through that the centre of a sphere and with the end points of the sphere is called diameter of the sphere.
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Given:
Diameter of the bowl = 10.5 cm
Inner Radius(r)=10.5/2= 5.25 cm
Curved surface area of the hemispherical bowl =
2πr²
= (2×22/7× 5.25 × 5.25)
= 173.25 cm²
Rate of tin plating is = ₹16 per 100cm²
cost of 1cm²= ₹16/100
Total cost of tin-plating the hemisphere bowl =
173.25 × 16/100
= ₹27.72
Hence, cost of tin plating on the the hemispherical bowl= ₹27.72
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Hope this will help you....