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Question

The cost of painting outer curved surface of a hollow hemispherical iron ball at rate of Rs. 2 per cm square is Rs. 1256. If thickness of the iron is 1 cm, find the cost of painting the inner curved surface of the ball.(Take π = 3.14).


A

Rs. 1076.32

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B

Rs. 2034.72

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C

Rs. 1017.36

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D

Rs. 508.68

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Solution

The correct option is C

Rs. 1017.36


The cost of painting outer curved surface of a hollow hemispherical iron ball at the rate of Rs. 2 per cm square is Rs. 1256. So, Outer curved surface area = 12562 = 628 cm2.

Then, curved surface area of hemisphere = 2π r2 = 628 cm2

r2 = 100 cm2

r = 10 cm

Now, thickness of iron = 1 cm. Therefore, inner radius = 9 cm.

Then, inner curved surface area = 2×227× 9×9 = 508.68 cm2.

So, cost of painting =508.6×2 = Rs. 1017.36 .


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