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If the radius of a circle be reduced by 50%. Its area is reduced by?

31.5%
39.5%
34.5%
65.5%

Correct Answer: 34.5%

Explanation:

Original area = π x (r/2)² = πr²/4
Reduction in area = π r² - 3π r²/4
∴ Reduction per cent = [ 3πr²/4 x 4/(πr²) x 100 ] %
= 75%

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