A) 420cm
B) 720m
C) 580m
D) None of these
Correct Answer: B
Solution :
Let the radius of the field be r. Then, \[\frac{1}{2}\pi {{r}^{2}}=30800\] \[\Rightarrow \,\,\frac{1}{2}\times \frac{22}{7}\times {{r}^{2}}=30800\] \[\Rightarrow \,\,{{r}^{2}}=30800\times 2\times \frac{7}{22}=19600\] \[\Rightarrowr=140\,M\] [taking positive square root] Thus, perimeter of the field \[=\pi r+2r\] \[=\frac{22}{7}\times 140+2\times 140\] \[=440+280=720\,m\]
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