A) 75 %
B) 50 %
C) 85 %
D) 65 %
E) None of these
Correct Answer: A
Solution :
Explanation \[\operatorname{Original} area\,\,=\,\,\pi {{r}^{2}}\] \[\operatorname{New}\,\,area=\,\,\pi {{(r/2)}^{2}}\,\,=\,\,(\pi {{r}^{2}})/4\] \[\operatorname{Reduction} in area=\,\,\left[ \pi {{r}^{2}}-\frac{\pi {{r}^{2}}}{4} \right]\,\,=\,\,\left( \frac{3\pi {{r}^{2}}}{4} \right)\] \[\operatorname{Reduction} \,percent=\,\,\frac{3\pi {{r}^{2}}}{\frac{4}{\pi {{r}^{2}}}\times 100}\,\,= 75\,%.\]
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